Structure and isomerisation of gaseous C3H8N+ metastable ions

Abstract

Five groups of structurally distinct C₃H₈N⁺(m/e 58) ions [(I) [graphic omitted]H₂·NH·CH₂·CH₃; (II)(CH₃)₂[graphic omitted]·NH₂; (III) CH₃·CH₂·[graphic omitted]H·NH₂; (IV) CH₃·[graphic omitted]H·NH·CH₃; (V)(CH₃)₂N·[graphic omitted]H₂] are generated in the mass spectrometer from 15 different amines and amides. Competing metastable abundance ratios are used to characterise the structure of the C₃H₈N⁺ ions which decompose with rate constants ca. 10⁵ s^–1. Three groups of ions are found: (II) and (III), and also (IV) and (V) decompose from the same structure, and ion (I) constitutes the third group. Extensive ²H and ¹³C labelling to generate specifically labelled ions of structures (I)–(V) yields information on (i) the structure of the decomposing ions, (ii) the extent of H and/or C scrambling, (iii) the mechanism of decomposition, and (iv) isotope effects. In view of the consistency with which the different C₃H₈N⁺ ions fall into their respective categories according to their structures, it should be possible to identify structural entities in unknown amines in terms of the metastable decompositions from m/e 58.