Skeletal rearrangement of metastable molecular ions of monosubstituted benzyl cyanides prior to elimination of [H, C, N], [H 2 , C 2 , N]˙ and [H, C, N, O]

The mechanism of [H, C, N) loss from metastable molecular ions of benzyl cyanides containing an F, Cl, CF 3 , CH 3 , HO or CH 3 O substituent was investigated by deuterium and 13 C labelling. The elimination of [H, C, N] from the metastable molecular ions of benzyl cyanides substituted with F, CI or CF 3 is preceded by randomization of the hydrogen atoms and tc some extent by a skeletal rearrangement of the CH 2 CN function, which leads to incorporation of the benzylic carbon atom in 20–30% of the expelled [H, C, N] molecules. By contrast, the metastable molecular ions of benzyl cyanides with a CH 3 , HO or CH 3 O substituent eliminate [H, C, N] molecules containing the intact cyano function and predominantly a hydrogen atom from fhe substituent. This preference for a hydrogen atom from the substituent irrespective of its position with respect to the CH 2 CN function is proposed to be the result of a rearrangement of the meta and para isomers to the ortho isomer possibly involving norcaradiene/cycloheptatriene radical cations. In addition to (H, C, N] loss, the metastable ions of o ‐, m ‐ and p ‐methoxybenzyl cyanide eliminate a [H 2 , C 2 , N]˙ radical consisting of the cyano function and the carbon atom and mainly two of the hydrogen atoms from the methoxy substituent. The occurrence of this reaction from the metastable ions of m ‐ and p ‐methoxybenzyl cyanide supports the indicated isomerization to the ortho configuration prior to dissociation. This skeletal rearrangement is manifested also in the loss of [H, C, N, O] from the metastable ions of m ‐and p ‐hydroxybenzyl cyanide.