Reactions of α,γ-unsaturated ketones, 4-dimethoxymethyl cyclohex-2-enones, and dicyclopentadienones are reported: (1) the predominant photorearrangements of cyclopent-2-enyl methyl ketones are multiplicity-specific 1,3-acetyl shift in the singlet excited state and 1,2-acetyl shift and cyclization in the triplet. The analogous phenyl ketones undergo cleavage to triplet benzoyl/cyclopentenyl radical pairs which are shown to both dissociate into free radicals and recombine and disproportionate within the triplet 'cage'. (2) The dimethoxymethyl cyclohexenones undergo specifically π → π* induced transformations: a 1,3-migration of the dimethoxymethyl substituent, and an abstraction of methoxyl hydrogen by the carbonyl oxygen which requires a distorted nonplanar geometry of the enone excited state. (3) Thermal and photochemical interconversions of three isomeric dicyclopentadienones are discussed which involve formal suprafacial 1,3- and 3,3-rearrangements.