Fragmentations of protonated benzaldehydes via intermediate ion/molecule complexes

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Abstract
Ions ap and am corresponding to protonated p‐ and m‐methoxymethylbenzaldehydes have been generated in a mass spectrometer by electron impact fragmentation of the correspondingly substituted 1‐phenylethanols (1 and 2). Metastable ions ap and am (2nd FFR of a VG‐ZAB‐2F mass spectrometer) react by elimination of CH3OH, loss of HCOOCH3, formation of ions CH2=OCH3 and to a small extent by loss of CH2O and CH3OCH3, respectively. The mechanisms of these reactions have been studied by extensive D‐labelling, and it is shown that these fragmentations are initiated by a transfer of the proton located originally at the carbonyl group onto the aromatic ring. The formation of ions \documentclass{article}\pagestyle{empty}$ {\rm CH}_2 = \mathop {{\rm OCH}_3 }\limits^ + $ and the loss of CH3OH occurs via π‐and σ‐complexes. The elimination of HCOOCH3 from ions ap and am corresponds to a functional group interaction between distal side chains and occurs via intermediate ion/molecule complexes formed by a protolytic cleavage of the formyl group. The loss of CH2O and CH3OCH3 proceeds also by intermediate ion/molecule complexes which are generated by a protolytic cleavage of the methoxymethyl side chain in ions ap and am.

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