Cyclization of α‐substituted α,ω‐diphenylalkyl carbenium ions: Reactivity of α‐trifluoromethylbenzyl cations vs. α‐methylbenzyl cations

Abstract

Abstract1‐(n‐Phenylalkyl)‐1‐trifluoromethylbenzyl cations and the α‐CH3‐substituted analogues were generated from the corresponding protonated benzyl alcohols by loss of H2O during chemical ionization (CI). The unimolecular reactions of these ions and of their derivatives specifically deuterated at the 1‐phenyl group were studied using the CI (methane) and CI (isobutane) mass spectra and the mass‐analysed ion kinetic energy spectra. The characteristic reaction giving rise to abundant ions in all the spectra is the elimination of C6H6 initiated by an electrophilic attack of the benzyl cation on the remote phenyl group. The α‐CH3‐ and α‐CF3‐substituted benzyl cations respond differently to the effect of internal excess energy on the intensity of the benzene elimination process and on the H–D exchange accompanying this process of the deuterated ions. This different reactivity of both series of ions demonstrates unambiguously that the α‐CF3‐substituted benzyl cations correspond to destabilized benzyl cations exhibiting the particular reactivity of ‘hot’ carbenium ions in the gas phase.