Under conditions of chemical ionization in the high pressure source of a mass spectrometer, the α-distonic CC ring-opened oxirane radical cation transfers a methylene group to 1,2-, 1,3- and 1,4-dichlorobenzene. The structures of the M + 14] ·+ product ions have been established by collisionally induced dissociation of these ions compared with reference ions and application of principal component analysis. 1,2-Dichlorobenzene yields 80% 2-chlorobenzyl chloride, 5% 2,3-dichlorotoluene and 15% 3,4-dichlorotoluene. The [M + 14] ·+ ions from 1,3-dichlorobenzene are 64–67% 3-chlorobenzyl chloride, 27–28% 2,6-dichlorotoluene and 7% 2,4- or 3,5-dichlorotoluene. From 1,4-dichlorobenzene mainly 4-chlorobenzyl chloride is formed, together with some 2,5-dichlorotoluene. In this case there is also an unidentified contribution, probably by 1,4-dichlorocycloheptatriene ions. Possible formation of distonic product ions does not occur in the cases of 1,2- and 1,3-dichlorobenzene, and from 1,4-dichlorobenzene it is considered to be unlikely.