Methyl loss from conventional and distonic isomers of C 3H 7N ·+

Abstract

The unimolecular reactions of a number of C 2H 5N ·+ and C 3H 7N ·+ isomers have been investigated. Mass-analyzed ion kinetic energy (MIKE) and collision-induced dissociation (CID) experiments as well as ab initio calculations show that the N-methylaziridine molecular ion and the distonic radical cation CH 2N(CH 3)CH 2 ·+ can interconvert below the threshold for unimolecular fragmentation, whereas the N-ethylmethylenimine molecular ion is structurally distinct. Likewise, the aziridine molecular ion can undergo ring opening below the threshold for unimolecular fragmentation. Methyl loss from the N-methylaziridine radical cation proceeds via isomerization to the distonic ion, whereas methyl loss from the imine radical cation is a straightforward simple cleavage. The heats of formation of the C 3H 7N ·+ and C 2H 5N ·+ isomers determined with four different composite methods, G2(MP2), G3, CBS-Q, and CBS-RAD, agree reasonably well, and reasonably well with the available experimental data. The distonic ions are found to be the more stable isomers on the C 2H 5N ·+ and C 3H 7N ·+ potential energy surfaces.