Hydrogen Rearrangements in the Mass Spectra of Alkylbenzenes

Abstract

By means of extensive deuterium labeling, the γ-carbon has been shown to be the principal site of transferred hydrogen (deuterium) regardless whether the hydrogen (deuterium) is primary, secondary, or tertiary. Although a significant transfer is also observed from the β, δ, ε, and more remote (to θ) carbons of the alkyl chain, such transfer is not attended by C–C cleavage (fragmentation) and is interpreted as an exchange between the aromatic ring ( ortho-hydrogen atoms) and the alkyl chain hydrogen atoms (deuterium atoms). The data herein also set small upper limits 011 the formation of m/ e 91 (C7H7+) from m/ e 92 (C7Hs+−) at both high and low ionizing voltages as well as in long and short alkyl chains.