Theoretical studies of substituent effects on stationary structures of amidine decomposition

Abstract

The unimolecular decomposition of substituted acetamidines XC(NH)NH₂, where X = CH₃(I), CH₂F (II), CHF₂(III), CF₃(IV), CH₂NH₂(V) and CH₂NO₂(VI) has been examined by ab initio methods using the 4-31G standard basis set. The process has an asynchronous mechanism. Transition structures for all the compounds can be described as four-membered rings. The influence of sub-stitution on the decomposition process is discussed in terms of a modified version of a More O'Ferrall–Jencks type diagram. The effects of functional groups are larger in a perpendicular than a parallel orientation to the reaction path; this is an example of the ‘anti-Hammond’ effect.