ORGANIC IONS IN GAS PHASE .23. LOSS OF CH3 FROM POLYMETHYLBENZENES

The mass spectra of a series of deuteriated polymethylbenzenes confirm and extend the model derived from labeled p‐xylenes for the loss of a methyl radical under electron impact. A methyl group flanked by two methyls undergoes no exchange before being lost. But one adjacent to an unsubstituted position appears to exchange with the o‐hydrogen atom via a methyl‐methylene‐methyl cycle. At least in p‐xylene, reformation of the methyl group may well be concerted with its loss. A similarly concerted coupling of CH2 and H and loss of the resultant methyl group could account for an apparent inconsistency between the mass spectra of methyl alkyl and phenyl alkyl ketones. Copyright © 1969 John Wiley & Sons, Ltd.