On the loss of a benzyl radical from the molecular ion of α,ω -dibenzyloxyalkanes : Evidence for a benzyl cation transfer in an SNi-type reaction,revealed by a simultaneous D- and 18O-labelling

The molecular ions of the title compounds appear to lose a benzyl radical, which must be due to the presence of two benzyloxy groups, as benzylalkyl ethers do not exhibit such an expulsion upon electron impact. The results of the partition of the labels deuterium and ¹⁸O in the ions m/e 107 (protonated benzaldehyde) and M-benzyl-benzaldehyde]⁺ put forward evidence that this process is initiated by a successive migration of a benzylic H atom to the opposite ether function and transfer of the benzyl cation from this protonated O atom to the uncharged O atom in an S_Ni-type reaction (cf Scheme 5).