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

A double rearrangement (hydrogen migration followed by carbon-carbon displa cement) constitutes the main fragmentation process of the 2-methoxydiphenyl methyl cations formed by benzylic cleavage of the molecular ion of ortho-me thoxy-substituted 1,1-diphenylalkanes 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 effec t. A geometry of the transition state, which accounts for the observed subs tituent effects, is proposed.