Competing oxygen migrations in ortho nitro aromatic thioamides on electron impact

Interesting competitive oxygen migrations from the nitro group to the nitrogen and to the sulfur have been noticed during the mass spectral decomposition of ortho nitro aromatic thioamides on electron impact. The migration of the oxygen to the nitrogen of the thioamide function results in the formation of stable o‐nitrosothiobenzoyl cation. The other novel ortho effect noticed in the ortho isomers is the transfer of an oxygen from the nitro group to the sulfur followed by the ejection of SO from the molecular ions. A mechanism involving the initial oxygen migration to the sulfur through a favourable 6‐membered transition state followed by cyclization with the concomitant expulsion of SO is proposed for this process. Other interesting decomposition processes occurring as a consequence of this ortho effect have also been noticed. The proposed mechanisms for these processes are supported by mass analysed ion kinetic energy spectra and high voltage scans. Copyright © 1983 Wiley Heyden Ltd.