Electron impact fragmentation of isomeric trimethylstannylnorbornenes and some related compounds

Abstract

The mass spectra at two or more ionizing voltages of the following compounds have been studied: norborn-2-enes with a trimethylstannyl substituent in the endo-5-, exo-5-, syn-7-, anti-7-, and 2-positions, 7-trimethylstannylnorborna-2,5-diene, 3-trimethylstannylnortricyclene, and syn- and anti-7-trimethylsilylnorborn-2-ene. A number of novel characteristics attributable to the bicyclic system and/or the double bonds have been observed. In contrast to organotin compounds previously studied, anti-7-trimethylstannylnorborn-2-ene shows a very large peak due to a hydrocarbon cation, C₇H₉⁺. This peak is very small, both in the spectrum of the syn- epimer and in those of the silyl analogues, and may be due to anchimeric assistance by the double bond in the loss of Me₂Sn from the ion Me₂SnC₇H₉⁺. The corresponding peak due to C₇H₇⁺ appears in moderate degree in the spectrum of 7-trimethylstannylnorborna-2,5-diene. Some evidence has also been obtained for intramolecular interactions between double bonds and positively charged in atoms in organotin cations.