Cation radicals of butene‐1, trans and cis butene‐2, isobutene, tetramethylethylene, cyclopentene, cyclohexene, butadiene, 1,3‐pentadiene, cyclopentadiene, 1,3‐ and 1,4‐cyclohexadienes have been produced mostly for the first time in γ‐irradiated frozen matrix of trichlorofluoromethane at 77 K. Well resolved ESR spectra at 77 K or at 130–155 K permit the determination of proton hyperfine coupling constants. Large hyperfine coupling constants of methylene and methyl protons adjacent to π electron systems indicate an extensive hyperconjugation in the cations. The following photoisomerizations are found: butene‐1+→butene‐2+, cyclopentene+→1,3‐pentadiene+, 1,4‐cyclohexadiene+→ 1,3‐cyclohexadiene+, 1,3‐cyclohexadiene+→1,3,5‐hexatriene+. The nonplanar cations of cyclopentene and 1,3‐cyclohexadiene undergo puckering motion in a limitedly warmed matrix. In the warmed matrix, where diffusions of the cation radicals toward unreacted hydrocarbon molecules proceed slowly, proton transfer reactions are induced. Decisive evidence for the formation of dimer cations is not obtained under the conditions studied.