Chlorine randomization between phenyl groups in the electron impact-induced fragmentation of polychlorinated biphenyls

The mass spectra of dichlorobiphenyls show chlorine randomization over both phenyl rings with the exception of 2,2′- and 2,6-biphenyl (I, e and f) in which both chlorine atoms are ortho to the Ph–Ph bond; similar results are obtained with tetrachlorobiphenyls which show chlorine randomization in the M– Cl2 ion.