Internal reactions of ion–neutral complexes from some disubstituted protonated benzaldehydes and acetophenones

Abstract

AbstractProtonated benzaldehydes ‘a’ and protonated acetophenones ‘b’, substituted by a methoxymethyl group, a hydroxy‐methyl group and a mercaptomethyl group, respectively, in position 3, in addition to a methoxymethyl side chain at position 5, have been prepared by electron impact induced dissociation from the corresponding benzylic alcohols. The spontaneous fragmentations of metastable ions of ‘a’ and ‘b’ have been investigated with the aid of specifically deuterated derivatives. Large signals arc observed for the loss of methanol induced by a proton migration across the aromatic ring. The competing loss of H2O and H2S, respectively, from the second side chain is less abundant, in agreement with the smaller PA's of HO and HS groups. The elimination of HCOX and CH3COX (X = OCH3, OH, SH), respectively, from ‘a’ and ‘b’ is also observed. The label distributions for these reactions are in agreement with a mechanism corresponding to an internal reaction of [CHO] + and [CH3CO] +, respectively, with the functional group of the side chains in an intermediary ion–neutral complex. In addition, fragmentations are observed arising from reactions between the two side chains at positions 3 and 5. The D labelling proves specific reactions without any H/D exchange and thus reaction channels separated from the methanol loss. The results are explained by internal ion‐molecule reactions in an intermediary ion‐neutral complex of a methoxymethyl cation, a hydroxymethyl cation and a mercaptomethyl cation, respectively, formed by a protolytic bond cleavage of the side chains.