Analogies Photochimiques. III—Diméthyl-4,4 allyl-2 Cyclohexanone. Elimination Inattendue de C2H4O et Perte de 15 Unités de Masse

The mass spectrum of 4,4-dimethyl 2-allyl cyclohexanone shows an ion at m/z 122 resulting from the elimination of a neutral acetaldehyde molecule direct from the molecular ion. Deuterium labelling results show a complex decomposition pathway during which four hydrogen atoms transfer to the eliminated acetaldehyde molecule. The molecular ion of this compounds also loses a methyl group originating from the allyl substituent. The mechanisms are discussed in terms of photochemical analogies.