An unexpected γ‐hydrogen rearrangement in the mass spectra of di‐<i>ortho</i> ‐substituted alkylbenzenes

Abstract

Abstract In contradiction of long‐accepted mass spectrometric dogma, the site‐specific γ‐hydrogen rearrangement is observed in alkylbenzenes in which both ortho positions are blocked with methyl substituents. Mass spectrometric studies of a series of five trimethyl‐ and three tetramethylisopentylbenzenes have shown that this rearrangement is only suppressed to a significant degree in those compounds in which all three positions ortho and para to the isopentyl group are blocked. Deuterium labelling has confirmed the γ‐site‐specific origin of the migrating H atom while metastable studies have been used to investigate the mechanism of the rearrangement process.