LOSS OF A METHYL RADICAL AND THE RETRO DIELS-ALDER REACTION IN THE ELECTRON-IMPACT MASS-SPECTROMETRY OF 2-CYCLOHEXEN-1-OL AND RELATED COMPOUNDS

The electron impact mass spectra of 2‐cyclohexen‐1‐ol and of several of its 2H and 13C labelled analogues show that the molecular ions lose a methyl radical by a completely different means from the mechanism described previously. Moreover, the retro Diels–Alder reaction also proceeds in a non‐classical way; in addition to the elimination of an olefinic molecule from unrearranged molecular ions, a second more important route implies a formal 1,3 allylic rearrangement prior to the retro Diels–Alder reaction. The mass spectra of a series of alkyl substituted homologues show that the competition between the two processes is closely related to the size of the olefinic moiety that is expelled. Copyright © 1979 John Wiley & Sons, Ltd.