Studies in organic mass spectrometry; Part 26. Unimolecular decomposition of ortho-methoxy-substituted diphenylmethyl cations

A double rearrangement (hydrogen migration followed by carbon–carbon displacement) constitutes the main fragmentation process of the 2-methoxydiphenylmethyl cations formed by benzylic cleavage of the molecular ion of ortho-methoxy-substituted 1,1diphenylalkanes with a wide range of internal energy. This has been demonstrated by recording mass analysed ion kinetic energy (MIKE) spectra, calculation of approximate activation energies (obtained by appearance energy difference) and calculation of a degrees-of-freedom effect. A geometry of the transition state, which accounts for the observed substituent effects, is proposed .