Principal EI-MS fragmentation pathways of phenylcyclopentadienyl cation 8a (m/z 243) formed from 2',3,5'-trichlorobiphenyl-4-yl ester 2,2,2-trichloroethyl ester 8. The fragmentation pattern resulting in the formation of 8a from the corresponding molecular ion is analogous to the pathways shown in Scheme 1.