View PDF Version
 
DOI: 10.1039/D5RP00089K (Paper) Chem. Educ. Res. Pract., 2025, Advance Article

Arrows first? – a qualitative exploration of how mechanistic organic chemistry is taught in the A-level curriculum in England†

Kristy L. Turner*ab, Nathan Owstona, Carl Poreea, Colin Evansa, Ali Mohammeda and Maha Khana
aUniversity of Manchester, Oxford Rd, Manchester, M13 9PL, UK. E-mail: kristy.turner@manchester.ac.uk
bBolton School Boys’ Division, Chorley New Rd, Bolton, BL1 4PA, UK

Received 11th March 2025 , Accepted 23rd July 2025

First published on 6th August 2025

Abstract

Student difficulties with the curly-arrow model in mechanistic organic chemistry have been the subject of a great deal of research. The inclusion of curly arrow mechanisms in an organic chemistry curriculum presents an opportunity for students to develop skills in problem solving which are useful both in higher education and employment so the topic has utility beyond content knowledge. An arrows first approach to organic mechanism has been suggested as an effective teaching strategy to prevent the development of misconceptions which may undermine a student's achievement and cause difficulties with further study. Through the lens of the A-level in chemistry, a regulated national qualification covering significant mechanistic chemistry content, we have evaluated a range of evidence to explore how mechanistic organic chemistry is taught. Taking a holistic overview of the curriculum we show that many aspects of the curriculum support an arrows first approach to teaching including the implemented and assessed curriculum, both influenced by examination boards. However we also found that a much larger proportion of teaching time, effort and assessment is devoted to case-study mechanisms, generally organised by functional group. These may be memorised by students, undermining an arrows first focus. Moreover, although we found our sample of teacher respondents were generally positive about teaching the fundamentals of the curly arrow model we also found a lack of accessible classroom resources and professional development to support teaching using an arrows first approach. In light of the published aims of the A-level in chemistry, this research has implications for policy and practice in the 16–18 chemistry curriculum for educators, examination boards and regulators.

Introduction

Curly arrows in organic chemistry

Mechanisms are used by chemists to explain or predict the outcome of reactions. They are an example of one of the many symbolic notations used in chemistry to connect the observed properties and behaviours of substances with the atoms and molecules which make them up. Organic reaction mechanisms use curved-arrow notation, often referred to by practitioners as simply ‘curly arrows’ (Clayden et al., 2001). Although they are now a dominant concept in organic chemistry, they are a relatively recent addition to the lexicon of symbolism in chemistry having recently celebrated their centenary (Ball, 2022). For many decades following their acceptance by the scientific community, using arrows to explain reaction mechanisms remained restricted to specialist papers. Curly arrows were first included in a textbook for teaching in 1953 (Andrés et al., 2016; Kramer, 2022) and it may be considered that they truly gained acceptance in the world of higher education with the publication of the classic textbook A Guidebook to Mechanism in Organic Chemistry by Sykes in 1961. Curly arrow mechanisms were first included in school level teaching in England in the 1980s, appearing in examination papers at A-level, the dominant qualification for 16–18 year olds in 1985.

Teaching and learning in mechanistic chemistry

Curly arrow mechanisms form the basis of much of the organic chemistry taught in universities. The pages of undergraduate organic chemistry textbooks are filled with a vast number and variety of mechanisms. Although many instructors in higher education will begin teaching from first principles it is important to recognise that the majority of students do not begin their undergraduate learning as empty vessels but bring with them their curriculum knowledge of organic chemistry and mechanism more specifically. It is recognised that in all subject areas students learn new ideas by linking those ideas to existing knowledge and organising knowledge into increasingly complex schemata (Madgwick, 2021). So it follows that understanding of curly arrow mechanisms in the 16–18 age range will influence transition to undergraduate study in chemistry. Indeed, in the most recent reform of the A-level, one of the objectives was to “define and assess achievement of the knowledge, skills and understanding which will be needed by students planning to progress to undergraduate study at a UK higher education establishment, particularly (although not only) in the same subject area.” (Ofqual, 2014).

However it is also important to recognise that the majority of students of A-level chemistry do not progress to chemistry degrees and school chemistry courses are not solely designed to prepare students to study chemistry at university (Reid et al., 2004). Indeed, the wide range of destinations in education and employment post-18 is one of the factors contributing to the popularity of the qualification. Beyond its merely transactional use as prior knowledge for further study, the curly arrow model of mechanism is a tool for students to develop skills in problem solving. Problem solving is an important skill set across all aspects of life (Queen and Cracolice, 2019) allowing individuals to achieve higher order thinking (Graulich and Lieber, 2020) which is important for success in education and employment (Mathematica, 2024). The development of “competence and confidence in a variety of practical, mathematical and problem solving skills” is one of the 5 aims and objectives outlined by the Department for Education for A-level science qualifications (Department for Education, 2014).

Mechanisms represent a model which fulfils the epistemic value of ‘simplicity’ in chemistry with Hoffman, Minkin and Carpenter arguing the application of the principle of Ockam's razor (Hoffmann et al., 1997; Erduran and Kaya, 2019). In all levels of instruction, simplifying conceptual matter, to make it appropriate for learning, is vital to the educational process (Taber, 2020). Clayden et al. state that the curly arrow is a simple and eloquent symbol for chemical reactions. Chemistry is highly conceptual with many abstract ideas, applying explanations based upon an invisible realm of entities. (Grove et al., 2012a,2012b; Andrés et al., 2016; Healy, 2019) Therefore, chemistry, in the context of academic study, will not appear in a school curriculum, it will be represented (Taber, 2020) and therefore this requires simplification of content. Essentially, curly arrow notation makes this critical connection between the physical and the ephemeral, serving as a ‘tool of simplicity’ in chemistry education. (Anderson and Bodner, 2008; Alvarez, 2012). These arrows provide an accessible and comprehensible representation of the reaction mechanism associated with an elementary reaction, ultimately allowing students to creatively approach unfamiliar reactions without the complexities of quantum theory. However this simplicity does not mean that students find the concept of curly arrows easy to apply. The difficulties students face with organic reaction mechanisms, forming the ‘learned curriculum’ have been the subject of a great deal of research in chemical education.

Caspari et al. (2018) states that “the questions of how and why processes occur are core questions of the natural sciences” and therefore that teaching students to reason mechanistically is a central goal of science education. However we know that teaching and learning often falls short of this goal in the curriculum structures of major education systems. Mechanistic organic chemistry is first encountered in the curriculum in England in the 16–18 phase when the majority of students study GCE A-level qualifications. Prior to this, organic chemistry in the 14–16 phase is often considered to be a memory test with students mainly learning ‘facts’ including reagents and conditions, reaction schemes and transformations (Turner, 2019). It may therefore follow that some students continue to take a similar, rote-learning, approach when learning mechanistic organic chemistry in later phases. Indeed, Read suggests that the emphasis on precision in drawing mechanisms in final examinations has made the rote-learning of mechanisms both possible and attractive (Read et al., 2012). A 2007 report by the Royal Society of Chemistry showed that some teachers will even ‘rote-teach’ mechanisms rather than approach them in a systematic way with an emphasis on electron flow (Bailey, 2007). Read's 2010 study of undergraduate students showed that students who underperformed in their 1st year organic chemistry had become accustomed to learning the precise details of how to draw the arrows in organic mechanisms in their A-level studies. They had attempted, mainly unsuccessfully, to use the same approach with the greater breadth and complexity of undergraduate mechanistic chemistry.

There is a wealth of research into the teaching and learning of organic mechanisms originating from researchers and practitioners worldwide. There are several qualitative studies showing that students at all levels of higher education encounter difficulties when using the curly arrow model to propose reaction mechanisms. These difficulties range from those fundamental in nature such as a failure to understand the basic purpose of the notation, to the more nuanced like how to use the curly arrow model effectively for problem-solving (Bhattacharyya and Bodner, 2005; Anderson and Bodner, 2008; Ferguson and Bodner, 2008; Kraft et al., 2010; Grove et al., 2012a; Bhattacharyya, 2014). Studies exploring student understanding of fundamental organic chemistry topics (Towns and Cruz-Ramirez de Arellano, 2014; Anzovino and Bretz, 2016), show that students possess gaps in their knowledge including classifying substances as nucleophiles and/or bases and accurately describing the steps that take place and the intermediates that are formed during the course of a reaction. A study of 2nd year college students in the USA on how students’ use of mechanisms changed over a course of study in organic chemistry showed the majority tended to present predicted products for reactions without showing a mechanism. Of those who did present some mechanistic reasoning, the authors considered many had simply ‘decorated’ the scheme with curved arrows after predicting a product. This was surprising and disappointing and the authors suggest that students required substantive feedback in order to properly develop their use of curly arrows (Grove et al., 2012a,2012b). These studies demonstrate that students lack the fundamental skills needed to solve mechanistic questions. However these studies mostly approach the topic through the lens of the student, observing and diagnosing student difficulties. Additionally there are reports of transformative redesign of organic chemistry curricula and their evaluation (Cooper et al., 2016, 2018, 2019) however these have been implemented within the flexibility of a college curriculum rather than a nationally defined, school-level qualification. Little has been found on the role of curriculum in its broadest sense in promoting the acquisition of skills in mechanistic organic chemistry and less still in the context of a curriculum designed at a national level.

Arrows first, mechanism focused and functional group sequencing

Literature reports suggests there are two contrasting approaches to the teaching of mechanistic organic chemistry. The functional group sequencing approach means mechanisms are taught as they are encountered in the teaching of the chemistry of a particular functional group. This may or may not be accompanied by specific instruction in the nature of the curly arrow model of mechanism. In contrast, in a ‘mechanisms first’ or ‘mechanisms focused’ approach, the instruction is focused around types of mechanism, this is always combined with an introduction to the principles of the curly arrow model, an ‘arrows-first’ approach.

The functional group approach is reported as leading to rote-memorisation of mechanisms without any accompanying understanding. This approach often results in complex concepts being taught before simpler ones because it is difficult to sequence the challenge of mechanisms within the rigidity of a scheme organised by functional groups (Anderson and Bodner, 2008). Moreover, classifying reactions by common names and mechanistic names within that framework gives the impression of new reaction types or opposing reactivity, for example nucleophilic and electrophilic addition (Flynn and Ogilvie, 2015). Evidence suggests that a mechanism focused curriculum is more successful in developing skills in mechanistic reasoning and shows signs of supporting better achievement in assessments.

Modifications to curricula to place greater emphasis on mechanistic thinking have been reported since the early 21st century. Early reports include modifying an existing, stable curriculum based around a popular textbook in several US colleges to include a unit on the fundamentals of mechanism prior to the formal introduction of organic reactions (Karty et al., 2007). This may represent a compromise position in curriculum change, taking an existing, well-resourced curriculum and making a specific change to enhance the teaching of mechanism. Karty et al. reported positive impacts in student competence in in-class tests and the standardised ACS examination as well as additional positive impacts on class morale, student evaluations of teaching and long-term retention of material.

As the body of evidence about student approaches to mechanisms grew a number of more ambitious curriculum changes were then reported. The earliest paper by Flynn in Canada reported the redesign of an organic chemistry course to place mechanisms before reactions and emphasise electron flow (Flynn and Ogilvie, 2015). Students experienced higher success rates with questions on both familiar and unfamiliar mechanisms and analysis of interviews showed that students were using electron pushing formalism correctly in their problem solving. Other indicators of success included ease of implementation, student and instructor satisfaction. This curriculum was later modified further to organise the material by the governing mechanistic pattern rather than by functional group and reaction name. Interviews of a sample of student experiencing this curriculum showed students attempting to map transformations, use charges and reason with relevant chemistry knowledge, even when they were unsuccessful in achieving the correct answer. A similar curriculum implemented by Lipton (2020) in the USA found that students maintained high scores throughout the semester rather than a sharp decline later in the semester which had previously been seen in a traditionally organised course. Grove et al., (2012a,2012b) showed an increase in success rates for students who use mechanistic reasoning in their approach to problems in organic chemistry and advises instructors to spend extra time on the basic principles of mechanism early in organic chemistry courses.

In the UK, Smith (2023) proposed a set of priority and selectivity rules to help students predict organic reaction mechanisms. This was evaluated within the context of part of an introductory course consisting of 5 lectures taught over a number of years in a UK university. Student feedback was outstanding with many students reflecting on the conceptual approach to reaction mechanisms being particularly effective. However crucially, Smith recognises that this approach can never lead to true mechanistic thinking if it is only a short course at the start of a degree. Instead, the approach needs to be integrated throughout a degree, something which is difficult to achieve in the complex environment of teaching in higher education where instruction is spread across numerous colleagues.

Difficulties in implementation of are also highlighted by Lafarge in his proposal of a new, mechanistically focused organic chemistry curriculum in French schools (Lafarge et al., 2014). The proposed curriculum was based around core principles and included greater emphasis on working out mechanisms from evidence including using data from studies of the physical chemistry of reactions. The authors highlight that a change in curriculum focus may be difficult to achieve, regardless of good intentions and evidence base, due to the requirements of the institution and exams, existing teaching habits of the workforce and a shortage of textbooks and resources to support the change. Indeed, instructors in US colleges interviewed by Nedungadi and Brown reported that they wanted to take a more mechanistic approach in their courses but the functional group approach demonstrated in textbook chapters was a barrier to this.

Although there is evidence that a mechanisms focused curriculum enhances student skills in reasoning and supports achievement in standardised tests, students will still make errors regardless of the organisation of the curriculum. This was explicitly reported by Galloway et al. (2017) and by Grove et al. (2012a,2012b) and also by Hermanns in Germany in evaluating a mechanisms focused course for pre-service teachers (Hermanns and Kunold, 2022). It is important to note that learning is inherently human and so it is not realistic to think that a curriculum change could lead to perfect learning in students. Indeed, errors are considered to be beneficial for learning in the long term (Metcalfe, 2017).

The A-level chemistry curriculum is not organised by mechanism types, the specifications for examinations have headings such as ‘alkanes, halogenoalkanes, alkenes’ as subheadings organising the content. Therefore in our study we focus on the common factor in those mechanistically organised curricula, the ‘arrows first’ approach where there is initial instruction in the fundamentals of the curly arrow model of mechanistic organic chemistry.

In this study we sought to answer two related questions.

• To what extent is mechanistic chemistry at A-level taught using an arrows first approach?

• How does the curriculum as a whole influence the teaching and learning of the fundamentals of organic mechanism with regards to the curly arrow model of electron movement?

A holistic overview of curriculum: an adaptation of the Cambridge framework

The Oxford English Dictionary defines curriculum as “a course; spec. a regular course of study or training, as at a school or university” (Oxford). There are numerous definitions of the word curriculum which may or may not agree with the common use of the term. A search of education literature widely available to teaching practitioners sees the word associated with other terms including ‘construction of curriculum’, ‘curriculum design’, ‘knowledge-rich curriculum’ and ‘curriculum coherence’ suggesting that the term curriculum tends to be used to refer to the statements about knowledge and skills found in documentation setting out the substantive and disciplinary knowledge of a subject (Burns, 2018; Myatt, 2018; Winter, 2018). Put simply, curriculum tends to be reduced to ‘content’ (Cambridge, 2017).

Kelly (2009) defines curriculum as the totality of student experiences that occur in the educational process. This broader definition incorporates the vital and crucially the human elements of curriculum. In order to provide a framework for individuals and institutions working in school improvement, researchers at Cambridge assessment drew upon a range of literature and international insights to propose levels of curriculum which can capture complex curriculum relationships (Cambridge, 2017). These are summarised as the intended, taught, learned, informal and unstated curriculum.

In the context of the A-level curriculum in England as regulated by Ofqual on behalf of the Department for Education (Department for Education, 2016), the intended curriculum is considered to be the subject content guidelines stated by the DfE in the last cycle of curriculum review in 2014. In England this guidance is then interpreted by the 4 examination boards (AQA, OCR, Eduqas and Pearson Edexcel) to form an A-level specification which is used by schools and teachers as a basis for their curriculum in chemistry. The A-level knowledge, understanding and skills defined by the DfE must comprise approximately 60% of an A-level specification. The remaining 40% is given over to examination boards to personalise their specification. This can be seen in the inclusion of particular topics by some exam boards but not others, for example the AQA examination board have used some of this flexibility to include the topic of biochemistry (protein structure and DNA bases) whereas the other examination boards do not cover this. Using the work of Van der Akker (2003) and Goodlad (1979) this interpretation of the intended curriculum introduces another level to the curriculum framework, termed the implemented curriculum.

GCE A-levels are the dominant qualification in the 16–18 qualifications market in England, Wales and Northern Ireland. For students in England a combination of 3 or 4 GCE A-levels is the most common qualification used for university entry. A-levels are assessed at the end of two years of study and in chemistry the final grade is determined by 100% written examination comprising 3 papers with a total assessment time of 6 hours. The A-level in chemistry therefore fits the definition of a high-stakes assessment (Unesco, 2009). High-stakes assessment are known to influence teacher behaviour and therefore the curriculum experience of students (Smith, 1991). The effect of exams on teaching practices and the experience of learners can be positive or negative. For example in Chen and Wei's 2015 paper there are several examples of teachers justifying their choices of classroom activity in chemistry based on whether related content will be in an examination (Chen and Wei, 2015). In a study in Turkey, 92% of teachers stated that their lesson content was selected with reference to their YGS and LYS exams which, like A-levels, are used as assessments for entry to higher education (Yaratan and First, 2013). One extreme of this may be the participants in Yaratan and First's study who admitted that the exams had a great influence on their teaching and they consider the topics that are likely and unlikely to be asked leading them to not teach some topics as shown by the quote ‘I eliminate the topics accordingly’.

This leads to the inclusion of another level in the framework, the assessed curriculum. The evolution of the framework is visualised in Fig. 1.


image file: d5rp00089k-f1.tif
Fig. 1 A diagram illustrating the evolution of the curriculum evaluation framework.

This framework has been used to review the coverage knowledge and skills associated with the topic of electrochemistry in chemistry curricula worldwide (Turner et al., 2024) and in policy reviews of the chemistry curriculum by the Royal Society of Chemistry (RSC, 2020). The informal (untaught experiences, enrichment activities, societies) and unstated curriculum (culture and ethos) are not significant in the context of a subject curriculum and so do not form part of the evaluation with regards to mechanistic chemistry.

It is important to note that this framework is not linear. While the intended curriculum, by design, influences 60% of the implemented curriculum the other curriculum levels are all influenced and in turn influence each other. This is crucial in understanding the nature of any interventions made as a result of this review, “policy may assume that things happen, but the realities in school can play out differently” (Cambridge, 2017).

Methodology

We sought to answer our research questions using the framework shown in Fig. 1 to evaluate the curriculum in mechanistic organic chemistry at A-level in England using a variety of sources of evidence. These sources of evidence are outlined in Table 1.
Table 1 A summary of the sources of evidence used in evaluating the A-level chemistry curriculum in mechanistic organic chemistry
• To what extent is mechanistic chemistry at A-level taught using an arrows first approach?
• How does the curriculum as a whole influence the teaching and learning of the fundamentals of organic mechanism with regards to the curly arrow model of electron movement?
Evidence Intended Implemented Assessed Taught Learned
Dept for Education. GCE AS/A level subject content x        
Exam specifications (2015)   x      
Assessment items (questions and mark schemes)     x    
Examiners’ reports     x   x
Textbooks   x   x  
Online study materials       x  
Survey responses     x x x
Interviews     x x x

The sources of evidence are described in greater detail below.

1. Review of syllabus documentation

The latest specifications (2015) from the exam boards OCR, AQA, Eduqas and Edexcel outline the learning objectives (ILOs) to be covered through the A-level course.

2. Review of popular textbooks and popular online resources

Textbooks are one example of a resource available to both teachers and students. From a research perspective textbooks provide a static, dated resource for analysis and as such have been used to provide insights into many aspects of chemistry education including the intended curriculum (Eilks et al., 2017), presentation of concepts (Bergqvist et al., 2013; Kapici and Savaşci-Açikalin, 2015; Upahi and Ramnarain, 2019), provision of questions (Sanger and Gilette, 2014), mistakes and misconceptions (Boulabiar et al., 2014; Gegios et al., 2016) and issues related to equality and diversity (Murray et al., 2022). Within organic chemistry they have been used in investigating the promotion of representational fluency and 2D/3D relationships (Dixon et al., 2013) and student ideas about the structure and function of nucleophiles and electrophiles (Anzovino and Bretz, 2016).

Murray et al. (2022) state that textbooks are an important aspect of students’ school lives although the popularity of textbooks as a learning resource has been declining in recent years (Turner and Chung, 2020). Despite this there is still considerable investment in the production and purchase of textbooks. Teachers may also use them as a resource in lesson preparation. 6 A-level textbooks were reviewed to evaluate their approach to explaining mechanism. These covered all of the A-level specifications considered in this research. A general textbook not related to a specific syllabus was also reviewed for completeness. Details of the textbooks evaluated can be found in Appendix A2 (ESI†).

3. Assessment items from published examinations in the period 2016–2022 and examiners reports

Both students and teachers have ready access to past paper questions and mark schemes. These may influence their approaches to teaching and learning.

Examiners reports are written after the marking completion is finished and contain observations by the examiner team on performance on the questions asked in a particular examination paper. They highlight where questions were particularly well done or where misconceptions or errors occurred.

4. Surveys

Teachers represent one of the very human elements of curriculum, they are key to the transformation of the intended and implemented curriculum into real classroom activities (Deng, 2018). Research suggests that the ways teachers engage with the curriculum has a greater influence on student outcomes than the curriculum materials themselves (Remillard, 2005). Within organic chemistry there may also be a persistent problem with how organic chemistry is taught with attitudes to learning passed from teacher to student (O’Dwyer and Childs, 2017). Therefore the interaction of teachers with the curriculum with regards to mechanism may affect how engaged students are with the fundamentals of curly arrow mechanisms. Surveys allow a larger population to be sampled relatively quickly. Four surveys were used to gain insight into the taught curriculum as summarised in Tables 2.

Table 2 A summary of the four surveys undertaken within this research
Survey Focus Order of implementation Notes
Extended survey Teaching population, the order of teaching mechanisms and approaches. 2 The results of this survey were used to inform the later ‘approaches’ and ‘order of teaching’ surveys.
Influences survey Factors influencing how teachers approach the teaching of curly arrow reaction mechanisms. 1  
Approaches survey Types of teaching activities teachers include in their initial teaching of curly arrow reaction mechanisms. 3  
Order of teaching The order of teaching of the 8 different mechanisms in the AQA specification. 4  

All surveys were deployed using a Google form. This reliable software ensured accessibility for teachers accessing the survey on a range of different devices. Surveys were distributed through the researchers’ established networks and social media, primarily X/Twitter where there was an active chemistry teaching community. All surveys were accompanied by instructions about informed consent and the storage and handling of the data arising from the participant responses. Surveys were scrutinised in the ethical approval stage.

Extended survey

Course syllabus documents, textbooks and web resources only show the intended curriculum. In their own classrooms teachers have considerable freedom in the teaching approaches they use and our extended survey sought to get an overview of this. The questions asked in this survey can be found in Appendix C of the ESI,† and are summarised as follows –

• Questions to establish the characteristics of the teacher participant population to check for sampling biases.

• Indication of teaching order.

• Questions about teaching approaches (the results from these questions informed the design of the ‘approaches’ survey).

• Recruitment for the interviews.

Influences survey

This short survey included 3 questions, all compulsory. The first two questions were multiple choice and probed the geographical location of participants and their teaching experience. This aimed to check eligibility within the parameters of the research. The main question in this survey was tick box, multiple completion and asked about the influences on teaching mechanistic organic chemistry. The available answers were designed using insights from the extended survey, discussion with experienced chemistry teachers and informed by the literature.

Approaches survey

This short survey had one compulsory question. Participants were presented with a list of 13 different teaching approaches. They were asked to rank them as approaches they would always, frequently, sometimes, rarely and never use when first teaching organic reaction mechanisms. The approaches presented in this list were decided upon from insights from the literature together with the extended survey and discussion with experienced chemistry teachers. The approaches given were direct instruction, Powerpoint slides, textbooks, videos, mini whiteboards, booklets, dual coding, mind maps, physical models, animations, past paper questions, partial completion exercises and spot the mistake activities.

Order of teaching

It became apparent from the extended survey that there were potentially interesting patterns in the order of teaching of particular mechanisms. However the extended survey was open to teachers of all exam boards so this separate order of teaching survey was designed to target teachers of the AQA specification. The AQA examination board specifies the teaching of the most mechanisms, seven curly arrow mechanisms in total so gives the most in-depth picture of the preferred order of teaching. This survey asked teachers of AQA A-level chemistry to indicate the order of teaching the seven mechanisms.

5. Interviews with A-level chemistry teachers.

Surveys may be limited in the insight they can offer. Interviews allow teachers to better explain their reasoning in some of the aspects of the research which was probed through review of documentation or short surveys. Participants for this stage of the research were identified through the extended survey. The interviews took place over Zoom and were recorded. Participants were informed of the recording and given the option to withdraw consent at this stage. Upon completion of the interviews the video file was deleted and the audio file processed using the Otter AI transcription suite. The interviews were semi-structured and interview questions can be found in Appendix D (ESI†).

Ethics statement. This project was considered under the University of Manchester's ethics policy, using the University's ethics decision tool. The study was deemed exempt from ethical approval as the work was evaluated as being a low-risk student project. This classification was applied as the surveys and interviews forming the study involved participants giving answers on subjects deemed to be within their professional competence. All university guidelines around maintaining anonymity and drafting questions to keep within the boundaries of this classification were followed. Surveys and interviews were carried out by student researchers with no relationship with the participants.

Results

Department for education guidance and exam specifications

GCE A-levels in sciences in England are regulated by OfQual on behalf of the Department for Education (DfE). During curriculum reform the DfE sets out the common subject content and this is then used by examination boards to draft their specifications. In England there are 4 examination boards offering a total of 5 different specifications for the A-level chemistry qualification. The most recent reform of A-level chemistry was in 2015.

The DfE guidance document is analogous to national curriculum guidelines and states a number of aims including equipping students with essential knowledge and understanding of different areas of the subject and encouraging them to develop enthusiasm and interest. The A-level knowledge, understanding and skills defined in the subject content documentation must comprise approximately 60% of an A-level specification. The remaining 40% is given over to examination boards to personalise their specification which accounts for the small differences between the content in different specifications.

At this, the highest level of curriculum oversight there is one statement related to mechanism. This states “mechanisms classified as radical substitution, electrophilic addition, nucleophilic substitution, electrophilic substitution and nucleophilic addition”. There is no indication in the subject content set out by the DfE as to whether the fundamentals of the curly arrow model should be taught.

All A-level chemistry specifications have learning objectives including statements about mechanism. The particular mechanisms required by each of the specifications varies. Read and Barnes summarised the reactions which are stipulated in each syllabus in their review of the 2015 specification changes (Barnes and Read, 2015). From this it is possible to distil the mechanisms required by each examination board. Excluding the ‘mechanism’ for free-radical substitution which requires no curly arrow notation, a minimum of 4 different mechanisms is studied in most specifications as shown in Table 3. The highest number of mechanisms, a total of 7 is required by the AQA exam board.

Table 3 The specific mechanisms required by the boards illustrating the minimum number of 4 and the maximum number of 7
  OCR A/OCR B AQA
Nucleophilic substitution (SN2) ✓ ✓
Electrophilic addition ✓ ✓
Elimination from a haloalkane   ✓
Elimination from an alcohol (H+ catalysed)   ✓
Electrophilic (aromatic) substitution ✓ ✓
Nucleophilic addition ✓ ✓
Nucleophilic addition–elimination   ✓

Both the OCR A and AQA specifications have learning objectives specifically related to the underlying principles of mechanisms that are outside of the specific context of a given mechanism or functional group. In both of these specifications these learning objectives are positioned before the mention of any specific mechanism, in an introductory or basic skills section. This is the clearest evidence that the specification suggests an arrows-first approach is taken. Table 4 shows an example of the wording of these objectives.

Table 4 Syllabus objectives about mechanism in the OCR A specification
4.1.1 basic concepts in organic chemistry
4.1.1 (g) The different types of covalent bond fission: a ‘curly arrow’ described as the movement of an electron pair, showing either heterolytic fission or formation of a covalent bond.
  Additional guidance: use of the ‘curly arrow’ model to demonstrate electron flow in organic reactions
4.1.1 (i) Reaction mechanisms, using diagrams, to show clearly the movement of an electron pair with ‘curly arrows’ and relevant dipoles.
  Additional guidance: any relevant dipoles should be included. Curly arrows should start from a bond, a lone pair of electrons or a negative charge

A less clear focus on fundamentals of curly arrow mechanisms is seen in the OCR B and Edexcel specifications. The OCR B specification takes a context-led approach to all concepts through the use of ‘chemical storylines’. Therefore, mechanisms are outlined as they come up in each context. However, the ‘colour by design’ storyline has a learning objective about the use of curly arrows in mechanism which is not related to a particular individual mechanism. The OCR B (Salters) specification is the only one to state the use of ‘half curly arrows’ in radical mechanisms.

The first mention of curly arrows in the Edexcel specification is within the context of the electrophilic addition of alkenes. In topic 6 organic chemistry, the statement “use of the curly arrow notation is expected – curly arrows should start from either a bond or from a lone pair of electrons” immediately follows the learning objective for the mechanism of alkenes and halogens, hydrogen halides and other given binary compounds. This statement acts as additional guidance on the teaching of the syllabus point related to electrophilic addition, it is not a syllabus objective.

Eduqas is the only specification which does not define the fundamentals of the curly arrow. Indeed there is no mention of the term ‘curly arrow’ or related terms anywhere in the syllabus document. The specification for Eduqas only mentions mechanism in the specific context of the mechanisms required e.g. 3.2 g Learners should be able to demonstrate and apply their knowledge and understanding of mechanism of electrophilic addition, such as in the addition of Br2 to ethene, as a characteristic reaction of alkenes. This suggests Eduqas takes a functional group approach to the teaching of mechanism.

None of the specifications have objectives in the area of physical organic chemistry which may support greater understanding of the steps in mechanisms (Carroll, 2023) such as observations of changes in stereochemistry or kinetic or isotopic labelling studies.

The specifications of OCR A and AQA have the largest market share of candidates for A-level chemistry. Therefore the majority of students moving onto higher education and employment will have encountered an implemented curriculum stating that the underlying principles of curly arrow mechanisms should be covered by their teachers. Interestingly when a comparison was made between the current (2015) specifications and the previous specification (2008) it was clear that objectives related to the curly arrow model of mechanistic chemistry have only been included in the most recent curriculum change. There were no objectives on this concept in the 2008 specifications for both of these examination boards.

Results: textbooks and online resources

The contents pages and index of textbooks was scrutinised to find sections relating to mechanism. This showed that there was alignment between the inclusion of objectives related to the fundamentals of mechanism within exam specifications and coverage of these concepts in textbooks.

For example in Lister and Renshaw, available in print and on the Kerboodle platform, there are two paragraphs of text titled reaction mechanisms and with the sub headings ‘curly arrows’ and ‘free radicals’. Here it is explained that the movement of a pair of electrons is shown by a curly arrow starting from a lone pair of electrons or covalent bond and that a curly arrow moves towards a positively charged area of a molecule and forms a new bond (Lister and Renshaw, 2015). This is however not exemplified with any examples or figures.

Pages on fundamentals of mechanism were also found on the popular websites Chemguide and Chemrevise. There is no specific video on the curly arrow model of mechanism on the MaChemGuy YouTube channel but there are many videos discussing how to approach questions with unfamiliar mechanisms.

Results: examination questions

A-levels in sciences make use of a number of different types of assessment items including multiple choice, tick box, fill in the blanks, short answer and longer answer questions. Examples of questions assessing the fundamentals of curly arrow mechanisms are found for those examination specifications that contain related learning objectives, AQA and OCR A. Moreover, different types of assessment items are used to test the objectives related to foundational principles in mechanism. A selection of assessment items, each classified as fundamental or taught mechanism for all the examination boards in this study can be found in Appendix B1 of the ESI.†

Questions have been explicitly asked about the nature of the curly arrow model; for example a question from the OCR A specification asked students “what does a curly arrow show in a reaction mechanism?” (OCR, 2019) There are also several examples of questions asking students to draw the products of a particular arrow movement. An example of this is shown in Fig. 2, cross referencing the specification and the examiner's report it is clear this is not a taught case-study mechanism.


image file: d5rp00089k-f2.tif
Fig. 2 A short answer question from the OCR A specification in 2019 which focuses on the fundamentals of curly arrow movements. ©OCR.

In contrast, assessment of mechanism in Eduqas shows a focus on curly arrows only in the context of individual taught mechanisms, further evidence that this exam board does not expect the fundamentals of arrow movement to be taught. For example, in the June 2018 Organic Chemistry and Analysis paper, students were asked to complete the electrophilic addition mechanism and in another question give the mechanism for the formation of 4-nitromethylbenzene from methylbenzene and the nitronium ion (Eduqas, 2018). Both of these question parts assess specific individual taught mechanisms referenced in learning objectives, C3.2g and OA1.2c respectively.

An analysis of the number of marks allocated to mechanisms across the examinations was carried out using examination papers from Jun 2019–June 2022. The detailed breakdown can be found in Appendix B2 (ESI†) and a summary is shown in Table 5.

Table 5 A summary of the mark allocation for mechanisms for the AQA and OCR A examinations from Jun 2019–Jan 2022
  Total mechanism marks Proportion of marks allocated to fundamentals of curly arrows (%) Number of individual mechanisms examined
AQA 11–17 (mean 13.5) 0–33.3 (mean 20.1%) 2–5 of max 7 (mode 3)
OCR A 9–15 (mean 12.5) 25–50 (mean 40.4%) 2 of max 4

The OCR A specification requires fewer taught mechanisms and consistently allocates more of the marks to questions assessing fundamental understanding of the curly arrow model. AQA requires knowledge of more mechanisms although overall the proportion of assessment allocated to mechanisms is similar. Their allocation of marks to questions assessing fundamentals is much more variable. In some years AQA has only assessed individual taught mechanisms with no marks allocated to fundamentals but in other years a third of marks has been for application of fundamentals.

An analysis of the 2021 papers for OCR A and AQA shows a remarkable similarity between the exam boards in the years where they both assess fundamentals and case study mechanisms. This can be found in Appendix B3 (ESI†). The analysis also shows relatively minor role that assessment items related to the fundamentals of mechanisms have in the overall examination with around 2% of the total marks for the qualification allocated to this.

Results: examiners reports

Examiners reports were accessed for those questions highlighted. Inductive coding of the comments on mechanistic questions did not show any definite trends however comments were made in some reports about lower achievers often writing arrows in the wrong direction or to the wrong atom or bond. The use of skeletal formulae in mechanistic outlines was also highlighted as being challenging whether that was for questions on fundamentals or taught mechanisms. A summary of the analysis can be found in Appendix E (ESI†).

Results: surveys

The majority of the respondents (84%) to the extended survey were teachers of the two specifications which make up the largest market share of A-levels in chemistry, AQA and OCR A. The participant teachers in the sample were mostly in the more experienced section of the teaching workforce with 4 classified as early career (0–2), 16 established (3–7), 29 experienced (8–14) and 33 very experienced (15+ years).

Order of teaching

A key finding of the extended survey is an insight into the order of teaching of individual mechanisms. In the order of teaching survey specifically targeting teachers of the AQA specification this was probed further. The order outlined in the specification is shown in Fig. 3. It should be noted that specification order is not a prescribed teaching order however teachers may choose to use it as such.
image file: d5rp00089k-f3.tif
Fig. 3 A schematic illustrating the order in which the implemented curriculum of mechanisms is presented in the AQA A-level chemistry specification.

Survey respondents (n = 50) reported 21 different routes through the mechanisms included in the AQA specification. While most (88%) survey respondents taught free radical substitution first, as in the specification, only 30% reported teaching mechanisms in the precise order set out in the AQA specification. An additional 10% of respondents teach the five (first year) mechanisms in specification order and then teach the remaining three mechanisms out of specification order. The second most common sequence (18%) starts with free radical substitution, electrophilic addition second (fourth on the specification), before reverting to specification order. No other sequence of mechanisms was taught by more than 6% of respondents.

Influences survey

The influences survey allowed participants to select up to 11 options of factors influencing their teaching of curly arrow mechanisms with the final option allowing a free text response. The teacher respondents (n = 40) chose 188 influences in total. Teacher responses showed different numbers of influences with a range from 1 influence (n = 1) to 9 influences (n = 1), a summary is shown in Fig. 4. The mean number of influences was 4.7 with a median of 5 and a mode of 5. The teacher's own subject knowledge and the learning objectives defined by the exam specification were equally the most significant influences on teachers’ delivery of mechanistic organic chemistry.
image file: d5rp00089k-f4.tif
Fig. 4 A visualisation of the factors influencing the teaching of curly arrow mechanisms at A-level as reported by a sample of 40 teachers.

Reported approaches to teaching

In the extended survey, all teachers reported an approach to teaching mechanism based on explanations of key concepts. Bonding, electronegativity, and bond enthalpy were all mentioned by a range of teachers in their free text responses as being significant for a good understanding of mechanism. A small but significant group of teachers (n = 13) reported the use of a standalone lesson on curly arrows before the teaching of mechanisms specific to the examples in their specification. This was reported by teachers across the spectrum of experience except early career teachers. For example, an arrows first approach was described by a teacher reporting 4 years of A-level teaching experience, currently delivering the AQA course. They described teaching an “intro lesson, what a curly arrow means, (using the) mechanisms sheet from the RSC”. A more established teacher with 10 years of experience, also delivering the AQA specification said they gave “definitions of words and arrows first, then match to the theory at that level”.

Only two teachers clearly stated that they did not teach the basics of curly arrow mechanisms before other mechanistic content. Both of these teachers deliver the AQA specification so this is in direct opposition to the outlined specification points on mechanisms. For example one teacher clearly outlined this stating they teach mechanistic principles “within the relevant content…rather than at the start of the course in an introduction to organic chemistry as the specification states”. They then describe the use of explanations alongside each mechanism required by the syllabus. Both teachers who reported this approach were relatively inexperienced, reporting 2 and 4 years of A-level teaching experience.

The biggest group of teachers mentioned the use of explanations alongside their teaching of mechanism but did not explicitly state they taught the fundamentals of mechanism first. The lack of clarity here informed the development of the questions used in the interviews.

Some teachers mentioned specific resources which they used to promote the understanding of mechanism itself including worksheets provided by the Royal Society of Chemistry (Royal Society of Chemistry, 2018) and a multimedia booster pack from the University of Southampton (Read, 2017). No teachers mentioned the use of experiments or practical work as a way of engaging students with this theoretical concept.

The range of teaching approaches mentioned in these free text responses was used to inform the design of the approaches survey which sought to get an overview of teaching activities. In this survey, participants (n = 33) were asked to report how often they used a variety of approaches in teaching curly arrow mechanisms, using a five-point Likert-type scale. The results demonstrate that direct instruction in curly arrow mechanisms is widespread (Fig. 5). All respondents reported using past paper questions when teaching students (73% “always”, 27% “frequently”). The widespread use of partial completion questions and “spot the mistake” problems (both >50% “frequently” or “always”).


image file: d5rp00089k-f5.tif
Fig. 5 A visualisation of teacher participants’ reported approaches to curly arrow mechanisms.

The survey data suggests that the use of molecular models is limited at this stage of students’ education, with 36% of respondents reporting never using them in class. The use of textbooks with in day to day teaching was also low with 61% of respondents use them rarely or not at all. Some respondents also provided examples of other approaches used in their classrooms. Two teachers reported doing in-class analysis and discussion of students’ responses to examination-type questions.

Results: interviews

11 teachers were interviewed and the audio transcripts were analysed by inductive coding. These teacher interviewees had a range of experience but tended towards the more experienced with only one being in the early career stage. A summary of teacher synonyms and coded interview summaries can be found in Appendix D (ESI†).

When teachers were asked about their own experience with organic mechanisms most remembered lots of repetition and recall when they were at school. Moira felt that she didn’t really understand mechanisms until she went to university and said “I don’t know if I really understood organic mechanisms when I was a kid. I was very good at drawing them because I was remembering”. Many of these teachers felt their understanding had increased while at university although 3 teachers felt that rote-learning of mechanisms had also been a feature of their university education.

All of the teachers mentioned instruction which supported understanding rather than rote-learning. A clear majority (10/11) of the teachers stated that they themselves took an approach which could be considered arrows first. They mention starting with introductory lessons focusing on electronegativity, the movement of electrons and key terminology and crucially that these lessons were taught before any formal introduction of the mechanisms specifically mentioned in their exam specifications. Interestingly, four teacher participants felt that other teachers within their subject departments did not teach for understanding and may encourage students just to rote learn mechanisms.

Some teachers (5/11) expressed frustration with the curriculum (as delivered in their school and/or as written in the specification) and its effect on the sequencing of ideas about mechanism. The placement of free-radical substitution as the first ‘mechanism’ was considered to be unhelpful to the development of mechanistic thinking given that it does not involve curly arrows and is instead represented as a series of equations.

There was no single challenge around mechanistic chemistry that the teachers all or mostly agreed with. The challenge most highlighted by the teachers (5/11) was the idea that mechanistic chemistry presented a kind of cognitive overload for students, bringing together many different concepts. Next most popular (4/11) was that students may like to or tend to memorise rather than strive for understanding. Other challenges mentioned by one or two teachers included a lack of understanding of key aspects (such as electronegativity), a lack of resilience or perseverance in students and a lack of attention to detail. Two teachers suggested only higher achievers could actually achieve understanding of mechanistic chemistry while one teacher mentioned that lower achievers really just needed to drill and memorise the familiar mechanisms.

There was relatively little reference to the influence of the examination and the examination board on the interviewed teachers’ practice. This could be linked to the bias of the sample, teachers who agreed to be interviewed about the teaching of curly arrow mechanisms may be more engaged in thinking about themes like conceptual understanding and curriculum sequencing. However a quote from Mark, a very experienced teacher stood out. He admitted his thoughts might be considered to be rather ‘non-educational’ but highlighted “it's a written exam with a pen, a bit of paper. And if you can't put the information that the marker wants to see on that paper, the fact you can describe it in all sorts of words, doesn't count, unless you score those marks. Learning stuff (about mechanism) doesn't score your marks, it's getting it down in a form that the examiner wants to see”. Additionally some teachers (4/11) noted that colleagues in their schools did not emphasise understanding in their teaching of mechanistic chemistry, instead telling students to ‘just learn the mechanisms’.

Discussion

The evidence analysed allows us to build a picture of the curriculum with regard to the teaching of curly arrow mechanisms in A-level chemistry using a framework of intended, implemented, taught, learned and assessed curricula. Our evaluation shows that at the highest level of curriculum oversight forming the intended curriculum, the guidance with regards to organic mechanisms is almost simultaneously vague and prescriptive. The guidance from the Department for Education makes no mention of the fundamentals of curly arrows but does state that 4 particular curly arrow mechanisms should be studied.

In their interpretation of this guidance for development of the specifications that make up the implemented curriculum, the approach taken by exam boards varies. A clear requirement to teach the fundamentals of the curly arrow model of mechanisms is seen in 2 of the 5 A-level specifications and these amount to the largest market share of candidates. Therefore the majority of students moving onto higher education and employment will have encountered an implemented curriculum stating that the underlying principles of curly arrow mechanisms should be covered by their teachers. In our influences survey we found that the learning objectives outlined by the exam board were the second most important influence on teacher practice, only marginally behind a teacher's own subject knowledge. The number of mechanisms taught also varies, with OCR A only including the 4 mechanisms required by the DfE guidance but AQA choosing to include many more; a total of 7.

However in both the major specifications the objectives about curly arrow fundamentals are followed by the study of a number of case study mechanisms, as many as 7 in the case of the AQA specification. This follows the same instructional routine described by Anderson and Bodner (Anderson and Bodner, 2008) who noted that students often receive a hidden message of a skewed balance in focus; that individual mechanisms receive more time from instructors and so must be more important. So, whilst the inclusion of objectives related to the fundamentals of curly arrow mechanism may be a positive step towards using an arrows-first approach, this may be ultimately undermined by the greater instructional time devoted to subsequent teaching of individual mechanisms.

Question setters, principal and chief examiners must take into account the learning objectives outlined in the specification in determining the coverage of assessment which at A-level is 100% closed-book, timed, written examination. Teachers and students may consider assessment items as good indicators of the approach specifications expect towards mechanisms, this is particularly true of high-stakes examinations. A-level examinations are high-stakes, the outcome of these examinations has substantial consequences for students, teachers and schools. The assessed curriculum is known to have an impact on the taught curriculum. This has been described as a ‘washback’ effect (Moore et al., 2024). If a concept is rarely assessed then teachers may place less emphasis on that concept in their teaching, an example of negative washback. There is evidence in the literature that teachers focus a significant proportion of their instructional efforts on helping students acquire the understanding and skills that will be tested in high-stakes examinations (Popham, 1987; Harlen, 2004). There may also be an effect on the learnt curriculum where students neglect concepts which are rarely assessed.

Since AQA and OCR A and B have learning objectives specifically related to the curly arrow model, it would be expected that assessment items will have been written to assess these across the lifetime of the specification. Evidence from published examination papers showed this, papers from AQA, OCR A and B all exemplify the learning objectives on the curly arrow model, outside of a specific taught mechanisms. A range of question types focusing on the fundamentals of curly arrows were seen across the sample taken from 2015–2022. For AQA and OCR A examinations the presence of assessment items focusing on the fundamentals of the curly arrow model could lead to a positive backwash effect, encouraging both the teaching and the learning of mechanistic thinking, however the bigger picture of the examinations needs to be examined.

The assessment of objectives around the fundamentals of the curly arrow model was inconsistent across the time period sampled. For example, AQA allocated no marks to assessing fundamentals in some examination cycles and the maximum marks for fundamentals in the sample was only one third of the total marks for mechanistic chemistry. This could lead to teachers and/or students interpreting these concepts as being less important and placing less emphasis on them in their teaching and learning. This kind of washback was rarely seen in our own interviewees primarily due to the bias in the sample however Mark was honest about his ‘non-educational’ ideas about just getting the mechanisms down on paper. Our surveys show how important past paper questions are to the taught curriculum, agreeing with the literature that assessment is an important influence on teaching practice in high stakes examination systems. A large proportion of teachers, 73% report that they always use past paper questions and 27% say they frequently use them when teaching curly arrow mechanisms. A significant proportion of teachers stated that assessment items influenced their teaching although none of the free text responses or interviews showed quite the negative backwash seen in some literature studies.

Approaches taken by textbooks and online resources were less influential on teacher practice. This is disappointing given that we found they were consistent with the examination specifications they were designed to align with. All of the textbooks we accessed included sections on the fundamentals of the curly arrow model for those specifications which included those objectives. It is important to note however that modern textbooks in England do not provide large selections of practice questions and exercises for teachers to draw upon in their teaching practice which may mean they have less utility for teachers in day to day teaching. Similarly although there was coverage of the concept this tended to be text based, often a single paragraph of explanation and not exemplified with appropriate visuals. Popular websites and YouTube channels also included sections on the curly arrow model but again, comparatively less space and time was devoted to this than to the individual taught mechanisms which could influence how students perceive the importance of this concept.

Beyond the textbooks there are relatively few examples of teaching resources to support teaching the fundamentals of mechanism although an example of a useful resource from the Royal Society of Chemistry's Education in Chemistry magazine was highlighted by some participants in surveys and interviews. This lack of suitable resources could be a barrier to implementing a curriculum more focused on mechanistic fundamentals (Lafarge et al., 2014; Negungadi and Brown, 2020). Our teacher interviewees, who were overwhelmingly ‘arrows-first’ in their approaches, mentioned designing their own ‘spot the mistake’ type exercises proving understanding of the curly arrow model and this was also highlighted in our surveys however in this case we were not able to discriminate between exercises focusing on fundamentals or on taught case-study mechanisms. While teacher agency and autonomy in choosing and designing their own learning materials is positively related to perceived self-efficacy and job satisfaction (Cribb and Gewirtz, 2007), additional workload generated due to a lack of useful resources for a particular topic may also be a source of stress.

Our teacher interviewees were able to give us an insight into how the approach of teachers may change across their teaching career. The majority of our interviewees mentioned rote learning as being a feature of their own school education and some felt it was also a feature of their university education in mechanistic chemistry. Just over a third of teacher interviewees stated that their approach had changed since they began teaching to include more emphasis on the fundamentals and some teachers changed their approach to be slower at the start of the topic. The influences survey showed that teacher subject knowledge was a key influence on teaching approaches in mechanistic chemistry, research shows that teachers with strong subject knowledge teach more effective lessons (Coe et al., 2014). It is therefore important to note the lack of professional development available for teachers in mechanistic organic chemistry. This is especially pertinent since the qualifications for entry to teacher training in chemistry requires a degree in a science-related subject with at least 50% of the content strongly related to chemistry (University of Manchester, 2025). A teacher of A-level chemistry in England may not have a degree in chemistry and may rely on their own experience from school which may have been focused on rote learning of mechanisms. The lack of professional development in this area reduces opportunities for teachers without a degree background to progress their practice with regards to the fundamentals of mechanisms. This may be particularly important as England is currently facing a shortage of chemistry teachers (Maisuria et al., 2023) and it is noted in research that England has on average some of the youngest (and therefore least experienced) teachers in the developed world (Cambridge Assessment, 2016) although shortages of chemistry teachers are also noted across Europe (Zainzinger, 2025).

Although not a focus of this study, our analysis of examiners reports and teacher interviews allow us a window into the learned curriculum. Errors in drawing intermediates were most frequently highlighted by examiners in answers to mechanistic questions even when those questions were considered to be answered well overall. This agrees with the observations of Towns and Cruz-Ramirez de Arellano (2014). Both examiners and teachers noted a lack of care in drawing curly arrows. Overall our teacher interviewees felt that mechanistic chemistry was challenging for students as it presented a cognitive overload, bringing lots of concepts together contributing to success in an individual mechanistic problem. Grove et al., (2012a,2012b) agrees with this, suggesting that “a dynamic equilibrium exists between the positive, organizational benefits of mechanism use and the more negative, cognitive load issues that its use engenders”. This balance between learning this chemistry with a clear focus on mechanistic reasoning and the elegance and simplicity that arrangement of a curriculum by functional groups presents is an interesting challenge for policy makers, curriculum specialists and educators working within a nationally designed framework.

Limitations of the research

This research draws upon the academic literature, curriculum documents and a broad sample of associated learning materials together with the opinions of surveyed teachers. It is important to highlight that teachers responding to surveys on the subject of mechanistic chemistry are likely to be those who are more engaged in thinking about issues related to the teaching of their subject for example, in reading subject related articles and engaging in discussions online and in professional fora. This is likely to be even more marked in teachers agreeing to give up their time to be interviewed.

Conclusions and implications for policy

Returning to the research questions we set out to answer, it is clear that the implemented curriculum written in the specifications studied by the majority of candidates taking A-level chemistry supports an arrows first approach to the teaching of mechanistic chemistry. These objectives were considered to be a significant influence on the teaching of this topic. There is also evidence that the taught curriculum also supports an arrows first approach with textbooks closely following the specifications and our sample of teachers all showing a clear bias for this approach. However there are relatively few resources (such as worksheets) for teachers to use with students to practise the skill of working with curly arrow mechanisms outside of taught, case-study mechanisms.

Teachers’ own subject knowledge was found to be a key influence on how teachers approach teaching mechanistic chemistry. A lack of continuing professional development focused on mechanistic chemistry limits the opportunities for teachers to engage with evidence and debate on effective methods of instruction in the fundamentals of the curly-arrow model. This deficit of professional development together with the lack of freely available resources for student practice may become more critical given the current pressures on the teaching workforce in England.

The assessed curriculum shows that the objectives around the fundamentals of the curly arrow model are assessed in A-level examinations however the proportion of assessment dedicated to this varies across examination boards and exam series. The two major exam specifications allocate a similar number of marks overall to mechanistic chemistry despite the difference in the number of individual mechanisms studied. This leads to OCR A consistently allocating a larger proportion of marks for application of the model to unfamiliar mechanisms. We found the assessed curriculum was an important influence on teacher practice, as is also reported in the literature. Greater physical space, in the specifications and in textbooks is dedicated to individual case study mechanisms which could be rote learned. The inconsistency of assessment together with the large number of case study mechanisms in some specifications may undermine efforts to focus student and teacher attention on the fundamentals of the curly arrow model and prevent a truly arrows first approach from being taken. Some insight into this was gained from our teacher interviewees who noted there were colleagues in their schools who encouraged students to memorise and replicate mechanisms.

The development of competence and confidence in problem solving is a stated aim of the A-level chemistry curriculum (AQA, 2015) and the inclusion of curly-arrow model of organic mechanistic chemistry has the potential to support this. In order to more consistently achieve these aims we would support curriculum changes to further enhance the arrows first approach to teaching organic mechanism, for example through reducing the number of taught case-study mechanisms and increasing the assessment of unfamiliar arrow sequences. However, there is significant interplay between the areas evaluated in our holistic overview of the curriculum in this area and hence any future efforts to reform the curriculum should not only focus on subject content but consider the many other aspects of curriculum that contribute to the student learning experience. It is important to remember that policy dictated by government is likely to look very different when implemented in schools (Cambridge, 2017). Any curriculum changes should be supported by professional development for new and established teachers and the development of appropriate, accessible teaching resources to facilitate a strong, arrows first, focus to organic mechanism.

Conflicts of interest

There are no conflicts of interest to declare.

Data availability

The data that support the findings of this study are openly available at DOI: https://doi.org/10.5281/zenodo.15623493.

Acknowledgements

We would like to thank the community of A-level chemistry teachers in England who gave up their time in answering surveys and participating in interviews.

References

  1. Alvarez S., (2012), Chemistry: A Panoply of Arrows, Angew. Chem., 51, 590–600 DOI:10.1002/anie.201101767.
  2. Anderson T. L. and Bodner G. M., (2008), What Can We Do About’Parker’? A Case Study of a Good Student Who Didn’t ‘Get’ Organic Chemistry, Chem. Educ. Res. Pract., 9, 93–101 10.1039/B806223B.
  3. Andrés J., Berski S. and Silvi B., (2016), Curly arrows meet electron density transfers in chemical reaction mechanisms: from electron localization function (ELF) analysis to valence–shell electron-pair repulsion (VSEPR) inspired interpretation, Chem. Commun., 52, 8183 10.1039/C5CC09816E.
  4. Anzovino M. E. and Bretz S. L., (2016). Organic chemistry students’ fragmented ideas about the structure and function of nucleophiles and electrophiles: a concept map analysis. Chem. Educ. Res. Pract., 17(4), 1019–1029 10.1039/c6rp00111d.
  5. AQA, (2015), AQA A-level chemistry Scheme of Assessment. https://www.aqa.org.uk/subjects/chemistry/a-level/chemistry-7405/specification/scheme-of-assessment (accessed January 2025).
  6. Bailey P., (2007), School to university transition: comparison of the A level specifications with year 1 at university, Royal Society of Chemistry (final report of the syllabus group from the Chemistry for our future project).
  7. Ball P., (2022), A Century of Curly Arrows, Chemistry World, Royal Society of Chemistry, https://www.chemistryworld.com/opinion/a-century-of-curly-arrows/4015168.article accessed Jan 2025.
  8. Barnes S. and Read D., (2015). Review of A level chemistry content. https://edshare.soton.ac.uk/14806/accessed September 2023.
  9. Bergqvist A., Drechsler M., De Jongb O., Chang S.-N. and Rundgren S., (2013), Representations of chemical bonding models in school textbooks – help or hindrance for understanding? Chem. Educ. Res. Pract., 14, 589 10.1039/C3RP20159G.
  10. Bhattacharyya G., (2014). Trials and tribulations: student approaches and difficulties with proposing mechanisms using the electron-pushing formalism, Chem. Educ. Res. Pract., 15(4), 594–609 10.1039/c3rp00127j.
  11. Bhattacharyya G. and Bodner G. M., (2005), “It gets me to the product”: How students propose Organic Mechanisms, J. Chem. Educ., 82, 1402–1406 DOI:10.1021/ed082p1402.
  12. Boulabiar A., Bouraoui K., Chastrette M. and Abderrabba M., (2014), A Historical Analysis of the Daniell Cell and Electrochemistry Teaching in French and Tunisian Textbooks, J. Chem. Educ., 81, 754 DOI:10.1021/ed081p754.
  13. Burns R., (2018), Applying the ‘powerful knowledge’ principle to curriculum development in disadvantaged contexts, Impact: Journal of the Chartered College of Teaching, 4, https://my.chartered.college/impact_article/applying-the-powerful-knowledge-principle-to-curriculum-development-in-disadvantaged-contexts/ (accessed January 2025).
  14. Cambridge, (2017), A Cambridge Approach to Improving education: using international insights to manage complexity. Cambridge Assessment, December 2017. https://www.cambridgeassessment.org.uk/cambridge-approach/improving-education/ (accessed Sept 2025).
  15. Cambridge Assessment, (2016), The average age of teachers in secondary schools. Data Bytes, Cambridge Assessment, July 2016 https://www.cambridgeassessment.org.uk/Images/312860-key-statistics-on-the-extended-project-qualification-2008-2015.pdf.
  16. Carroll F. A., (2023), Perspectives on Structure and Mechanism in Organic Chemistry, London: John Wiley & Sons. ISBN: 978-1-118-21088-8.
  17. Caspari I., Kranz D. and Graulich N., (2018), Resolving the complexity of organic chemistry students' reasoning through the lens of a mechanistic framework, Chem. Educ. Res. Pract., 19, 1117–1141 10.1039/C8RP00131F.
  18. Chen B. and Wei B., (2015), Examining chemistry teachers' use of curriculum materials: in view of teachers' pedagogical content knowledge, Chem. Educ. Res. Pract., 16, 260–272 10.1039/C4RP00237G.
  19. Clayden J., Greeves N., Warren S., Wothers P., (2001), Organic Chemistry, Oxford University Press, Oxford pp. 115–117.
  20. Coe R., Aloisi C., Higgins S. and Major L. E., (2014), What makes great teaching? Review of the underpinning research, https://www.suttontrust.com/wp-content/uploads/2014/10/What-Makes-Great-Teaching-REPORT.pdf (Accessed January 2025).
  21. Cooper M. M., Crandell O. M., Kouyoumdjian H. and Underwood S., (2018), Reasoning about Reactions in Organic Chemistry: Starting It in General Chemistry, J. Chem. Educ., 96, 213–226 DOI:10.1021/acs.jchemed.8b00784.
  22. Cooper M. M., Kouyoumdjian H., Underwood S., (2016), Investigating Students’ Reasoning about Acid–Base Reactions, J. Chem. Educ., 93, 1703–1712 DOI:10.1021/acs.jchemed.6b00417.
  23. Cooper M. M., Stowe R. L., Crandell O. M. and Klymkowsky M. W., (2019), Organic Chemistry, Life, the Universe and Everything (OCLUE): A Transformed Organic Chemistry Curriculum, J. Chem. Educ., 96, 1858–1872 DOI:10.1021/acs.jchemed.9b00401.
  24. Cribb A. and Gewirtz S., (2007), Unpacking autonomy and control in education: some conceptual and normative groundwork for a comparative analysis, Eur. Educ. Res. J., 6(3), 203–213 DOI:10.2304/eerj.2007.6.3.203.
  25. Deng Z., (2018), Pedagogical content knowledge reconceived: bringing curriculum thinking into the conversation on teachers' content knowledge, Teaching Teacher Educ., 72, 155–164 DOI:10.1016/j.tate.2017.11.021.
  26. Department for Education, (2014), GCE AS and A level subject content for biology, chemistry, physics and psychology April 2014 https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/593849/Science_AS_and_level_formatted.pdf.
  27. Department for Education, (2016), GCE Subject Level Conditions and Requirements for Science (Biology, Chemistry, Physics) and Certificate Requirements, Ofqual, May 2016. https://assets.publishing.service.gov.uk/media/5a81da4e40f0b62305b9127a/gce-subject-level-conditions-and-requirements-for-science.pdf (accessed January 2025).
  28. Dixon B. L., Bartlett F., Olimpo J. T. and Kumi B. C., (2013), Evaluating the effectiveness of organic chemistry textbooks in promoting representational fluency and understanding of 2D–3D diagrammatic relationships, Chem. Educ. Res. Pract., 14, 177 10.1039/C3RP20166J.
  29. Eduqas, (2018), CHEMISTRY – A level component 2 Organic Chemistry and Analysis https://pastpapers.download.wjec.co.uk/s18-8411-02.pdf (accessed June 2023).
  30. Eilks I., Khaddoor R. and Al-Amoush S., (2017), A comparative analysis of the intended curriculum and its presentation in 10th grade chemistry textbooks from seven Arabic countries, Chem. Educ. Res. Pract., 18, 375 10.1039/C6RP00186F.
  31. Erduran S. and Kaya E., (2019), Transforming Teacher Education Through the Epistemic Core of Chemistry, in Clough M. P., (ed.), Empirical Evidence and Practical Strategies. Cham, Switzerland: Springer, pp 25–49, https://link.springer.com/book/10.1007/978-3-030-15326-7.
  32. Ferguson R. and Bodner G. M., (2008). Making sense of the arrow-pushing formalism among chemistry majors enrolled in organic chemistry, Chem. Educ. Res. Pract., 9(2), 102–113 10.1039/b806225k.
  33. Flynn A. B. and Ogilvie W. W., (2015), Mechanisms before reactions: a mechanistic approach to the organic chemistry curriculum based on patterns of electron flow, J. Chem. Educ., 92, 803–810 DOI:10.1021/ed500284d.
  34. Galloway K. R., Stoyanovich C. and Flynn A. B., (2017), Students' interpretations of mechanistic language in organic chemistry before learning reactions, Chem. Educ. Res. Pract., 18, 353–374 10.1039/C6RP00231E.
  35. Gegios T., Salta K. and Koinis S., (2016), Investigating high-school chemical kinetics: the Greek chemistry textbook and students’ difficulties, Chem. Educ. Res. Pract., 18, 151 10.1039/C6RP00192K.
  36. Goodlad J. I., (1979), Curriculum Inquiry: The Study of Curriculum Practice, New York: McGraw-Hill.
  37. Graulich N. and Lieber L., (2020), Thinking in Alternatives—A Task Design for Challenging Students’ Problem-Solving Approaches in Organic Chemistry, J. Chem. Educ., 97(10), 3731–3738 DOI:10.1021/acs.jchemed.0c00248.
  38. Grove N. P., Cooper M. M. and Cox E. L., (2012a). Does mechanistic thinking improve student success in organic chemistry? J. Chem. Educ., 89(7), 850–853 DOI:10.1021/ed200394d.
  39. Grove N. P., Cooper M. M. and Rush K. M., (2012b). Decorating with Arrows: Toward the Development of Representational Competence in Organic Chemistry, J. Chem. Educ., 89, 844–849 DOI:10.1021/ed2003934.
  40. Harlen, W., (2004). A systematic review of the evidence of the impact on students, teachers and the curriculum of the process of using assessment by teachers for summative purposes (Research Evidence in Education Library), EPPI-Centre, Social Science Research Unit, Institute of Education.
  41. Healy E. F., (2019), Should Organic Chemistry Be Taught as Science? J. Chem. Educ., 96, 2069–2071 DOI:10.1021/acs.jchemed.9b00122.
  42. Hermanns J. and Kunold H., (2022), Mechanism comics as a task in a written exam in organic chemistry for pre-service chemistry teachers, Chem. Teacher Int., 4(3), 259–269 DOI:10.1515/cti-2021-0035.
  43. Hoffmann R., Minkin V. I. and Carpenter B. K., (1997), HYLE – Int. J. Philosophy Chem., 3, 3–28, https://www.hyle.org/journal/issues/3/hoffman.pdf.
  44. Kapici H. Ö. and Savaşci-Açikalin F., (2015), Examination of visuals about the particulate nature of matter in Turkish middle school science textbooks, Chem. Educ. Res. Pract., 16, 518 10.1039/C5RP00032G.
  45. Karty J. M., Gooch G., Gray Bowman B., (2007), Teaching a Modified Hendrickson, Cram, and Hammond Curriculum in Organic Chemistry, J. Chem. Educ., 94(7) 1079–1232 DOI:10.1021/ed084p1209.
  46. Kelly A. V., (2009). The Curriculum: theory and practice, 6th edn, ISBN 9781847872746.
  47. Kraft A., Strickland A. M. and Bhattacharyya G., (2010). Reasonable reasoning: multi-variate problem-solving in organic chemistry, Chem. Educ. Res. Pract., 11(4), 281–292 10.1039/c0rp90003f.
  48. Kramer K., (2022), Explainer: why are curly arrows used in organic chemistry? Chemistry World, Royal Society of Chemistry, https://www.chemistryworld.com/news/explainer-why-are-curly-arrows-used-in-organic-chemistry/4016507.article accessed Jan 2025.
  49. Lafarge D. L., Morge L. M., Méheut M. M., (2014), A New Higher Education Curriculum in Organic Chemistry: What Questions Should Be Asked? J. Chem. Educ., 91, 173–178 DOI:10.1021/ed300746e.
  50. Lipton M. A., (2020), Reorganization of the Organic Chemistry Curriculum to Improve Student Outcomes, J. Chem. Educ., 97(4), 960–964 DOI:10.1021/acs.jchemed.9b00606.
  51. Lister T. and Renshaw J., (2015), AQA Chemistry – A level year 1 and AS, 2nd edn, Oxford: Oxford University Press, p. 180.
  52. Madgwick H., (2021), EEF Blog: ECF– Exploring the Evidence: Prior knowledge and Pupil Misconceptions. https://educationendowmentfoundation.org.uk/news/eef-blog-ecf-exploring-the-evidence-prior-knowledge-and-pupil-misconceptions accessed Feb 2025.
  53. Maisuria A., Roberts N., Long R. and Danechi S., (2023), House of Commons Library, Teacher recruitment and retention in England, December 2023. https://researchbriefings.files.parliament.uk/documents/CBP-7222/CBP-7222.pdf.
  54. Mathematica, (2024), Education to Workforce Indicator Framework, https://educationtoworkforce.org/indicators/higher-order-thinking-skills accessed Feb 2025.
  55. Metcalfe J., (2017). Learning from errors, Annu. Rev. Psychol., 68, 465–489.
  56. Moore A. M., Fairhurst P., Bennett J. M., Harrison C., Correia C. F. and Durk J., (2024), Assessment and practical science: identifying generalizable characteristics of written assessments that reward and incentivise effective practices in practical science lessons, Int. J. Sci. Educ., 46, 643–669 DOI:10.1080/09500693.2023.2253366.
  57. Murray C., Anderson Y., Simms C. H. and Seery M. K., (2022), Representations of women and men in popular chemistry textbooks in the United Kingdom and Republic of Ireland, Chem. Educ. Res. Pract., 23, 373 10.1039/D1RP00187F.
  58. Myatt M., (2018), Building curriculum coherence, Impact: Journal of the Chartered College Teaching, 4, https://my.chartered.college/impact_article/building-curriculum-coherence/ (accessed January 2025).
  59. Negungadi S. and Brown C. E., (2020), Thinking like an electron: concepts pertinent to developing proficiency in organic reaction mechanisms, Chem. Teacher Int., 3(1), 9–17 DOI:10.1515/cti-2019-0020.
  60. OCR, (2019), https://www.ocr.org.uk/Images/621247-question-paper-synthesis-and-analytical-techniques.pdf.
  61. O’Dwyer A. and Childs P. E., (2017), Who says Organic Chemistry is Difficult? Exploring Perspectives and Perceptions, EURASIA J. Math. Sci. Tech. Ed., 13(7), 3599–3620.
  62. Ofqual, (2014), An Update on the Reforms Being Made to AS Qualifications and A Levels (Ofqual/14/5405) April 2014 https://www.gov.uk/government/publications/update-on-the-reform-of-as-and-a-levels (Accessed January 2025).
  63. Oxford English dictionary https://www.oed.com/dictionary/curriculum_n?tab=factsheet#7556257 (accessed January 2025).
  64. Popham W. J., (1987). The merits of measurement-driven instruction, Phi Delta Kappan, 68(9), 679–682.
  65. Queen M. S. and Cracolice M. S., (2019), Facilitating the Development of Students’ Problem-Solving Skills via Active Learning in General Chemistry, ACS Symp. Ser., 1340 DOI:10.1021/bk-2019-1340.ch003.
  66. Read D., (2017). Organic Reaction Mechanism Learning and Revision: Student Booster Pack, University of Southampton, https://edshare.soton.ac.uk/18496/ (accessed Jan 2025).
  67. Read D., Brown R. C. D. and Hinks J. D., (2012), A blended learning approach to supporting students in organic chemistry: methodology and outcomes, New Directions, 8, 33–37.
  68. Reid N., Hill R. A. and Hassan A. K., (2004), Ideas Underpinning Success in an Introductory Course in Organic Chemistry, U. Chem. Ed., 8, 40.
  69. Remillard J. T., (2005), Examining Key Concepts in Research on Teachers’ Use of Mathematics Curricula, Rev. Educ. Res., 75(2), 211–246.
  70. Royal Society of Chemistry, (2018), https://edu.rsc.org/ideas/end-curly-arrow-anxiety/3008691.article.
  71. Royal Society of Chemistry, (2020), The elements of a successful chemistry curriculum: Our vision for 11–19 chemistry education, https://www.rsc.org/policy-evidence-campaigns/chemistry-education/education-reports-surveys-campaigns/chemistry-curriculum-framework/.
  72. Sanger M. J. and Gilette G., (2014), Analysing the distribution of questions in the gas law chapters of secondary and introductory college chemistry textbooks from the United States, Chem. Educ. Res. Pract., 15, 787 10.1039/C4RP00115J.
  73. Smith M. L., (1991), Put to the test: The effects of external testing on teachers, Educ. Res., 20(5), 8–11 DOI:10.3102/0013189X020005008.
  74. Smith D. K., (2023), Priority and Selectivity Rules To Help Students Predict Organic Reaction Mechanisms, J. Chem. Educ., 100, 1164–1178 DOI:10.1021/acs.jchemed.2c00950.
  75. Taber K. S., (2020), Conceptual confusion in the chemistry curriculum: exemplifying the problematic nature of representing chemical concepts as target knowledge, Found. Chem., 22, 309–334 DOI:10.1007/s10698-019-09346-3.
  76. Towns M. and Cruz-Ramirez de Arellano, D., (2014), Students' understanding of alkyl halide reactions in undergraduate organic chemistry, Chem. Educ. Res. Pract., 15, 501–515 10.1039/C3RP00089C.
  77. Turner K., (2019), Teaching organic mechanisms, Education in Chemistry, Royal Society of Chemistry, https://edu.rsc.org/ideas/teaching-organic-mechanisms/3010691.article (accessed Jan 2025).
  78. Turner K. L. and Chung H., (2020), Transition to eBook Provision: A Commentary on the Preferences and Adoption of eBooks by Chemistry Undergraduates, J. Chem. Educ., 97(5), 1221–1225, https://pubs.acs.org/doi/10.1021/acs.jchemed.9b01157.
  79. Turner K. L., He S., Marchegiani B., Read S., Blackburn J., Miah N. and Leketas M., (2024), Around the world in electrochemistry: a review of the electrochemistry curriculum in high schools, J. Solid State Electrochem., 28, 1361–1374 DOI:10.1007/s10008-023-05548-0.
  80. Unesco, (2009), Unesco International Institute for Educational Planning, Learning Portal Glossary, https://learningportal.iiep.unesco.org/en/glossary/high-stake-assessment (accessed January 2025).
  81. University of Manchester, (2025), PGCE Secondary Chemistry/Entry requirements, https://www.manchester.ac.uk/study/masters/courses/list/11520/pgce-secondary-chemistry/entry-requirements/#course-profile (Accessed January 2025).
  82. Upahi J. E. and Ramnarain U., (2019), Representations of chemical phenomena in secondary school chemistry textbooks, Chem. Educ. Res. Pract., 20, 146–159 10.1039/C8RP00191J.
  83. Van der Akker J., (2003), Curriculum Perspectives: An Introduction, in Van der Akker J., Kuiper W. and Hamever U., (ed.) Curriculum Landscapes and Trends, Dordrecht: Springer-Science + Business Media, B.V., pp. 1–10 DOI:10.1007/978-94-017-1205-7.
  84. Winter M., (2018), A theoretical look at how to incorporate cognitive research into subject curriculum design, Impact: Journal of the Chartered College of Teaching, 2, https://my.chartered.college/impact_article/a-theoretical-look-at-how-to-incorporate-cognitive-research-into-subject-curriculum-design/ (accessed January 2025).
  85. Yaratan H. and First H. B., (2013), Impact of External Examinations on High School Curricula: Perceptions of Teachers and Students, Egitim Arastirmalari-Eurasian J. Educ. Res., 53(A), 1–18.
  86. Zainzinger V., (2025). Is Europe Running out of Chemistry Teachers? ACS Cent. Sci., 11(2), 173–176 DOI:10.1021/acscentsci.5c00038.

Footnote

† Electronic supplementary information (ESI) available: This is summarised as: Appendix A: Evidence from examination specifications and associated textbooks and online resources. Appendix B: evidence related to assessment. Appendix C: Summary of survey questions. Appendix D: Evidence from interviews. Appendix E: Evidence from examiners reports. See DOI: https://doi.org/10.1039/d5rp00089k
This journal is © The Royal Society of Chemistry 2025
Click here to see how this site uses Cookies. View our privacy policy here.