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Issue 6, 1999

Intramolecular benzyl–benzyl interactions in protonated benzyl diethers in the gas phase. Effects of internal hydrogen bonding

Abstract

Protonated molecules of a variety of benzyl diethers, produced by chemical ionization (CI), undergo a unique rearrangement yielding relatively abundant m/z 181 C14H13+ ions, both in the ion source and under collision-induced dissociation (CID) conditions. This highly general rearrangement involves an intramolecular C–C bond formation between the two benzyl groups, and the resulting C14H13+ ions have been shown by the analysis of their CID spectra to be an almost equimolar mixture of isomeric α-o-tolylbenzyl, α-p-tolylbenzyl and p-benzylbenzyl cation structures in all cases. This structural information suggests that this process may be viewed as gas-phase aromatic substitution of the non-charged benzyloxy group by the benzyl cation originating from the protonated ether function involving a series of π- (and/or ion–neutral) and σ-complexes. The extent of this fragmentation in alkane benzyl diethers PhCH2O(CH2)nOCH2Ph (n = 2–10,12) is strongly affected by the alkane chain length. Stereoisomeric benzyl diethers display an unusual steric effect: the trans-isomers give rise to more abundant C14H13+ ions than their cis-counterparts. The latter two effects are explained in terms of intramolecular hydrogen bonding between the two alkoxy groups. Bis(benzyloxy)benzenes and -naphthalenes exhibit very low abundance C14H13+ ions in contrast to the aliphatic analogues. This behavior is attributed to competing intramolecular benzylation involving the aromatic skeletons of these compounds.

Article information


J. Chem. Soc., Perkin Trans. 2, 1999, 1095-1106
Article type
Paper

Intramolecular benzyl–benzyl interactions in protonated benzyl diethers in the gas phase. Effects of internal hydrogen bonding

M. Edelson-Averbukh, A. Etinger and A. Mandelbaum, J. Chem. Soc., Perkin Trans. 2, 1999, 1095 DOI: 10.1039/A901622H

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