The rearrangement reactions following electron ionization in a number of aryl substituted conjugated nitriles have been studied using labelled compounds and collisional activation (CA) spectroscopy. The results indicate that a- phenyl cinnamonitriles and 9,1Bdihydro-9-cyanophenanthrene rearrange to a common intermediate which loses CH,' or CH,CN to give the ions at m/z 190 and 165. The CA spectrum of the deuterated analogue (compound 2)
shows that there is a complete hydrogen scrambling prior to the loss of the CH,' radical. The fluoroderivatives (compounds 5 and 6) behave similarly to the parent nitrile. The introduction of chlorine or bromine into the aromatic ring alters the fragmentation pattern and the only favoured decomposition pathway is the loss of a halogen radical. The CA spectra of the doubly charged ions at m/z 102 and 88 are also discussed. The CA spectrum of the MC' ion l,l-dicyano-2-phenyI ethylene is characterized by the presence of a rearrangement ion at m/z 103 (PhCN"). Others 177 (211, 176 (15). 151 (8), 102 (10). 88 (15) 178 (17). 177 (15). 152 (7), 102.5 (8), 88.5 (8) 177 (17), 176 (13). 151 (8), 102.5 (71, 88 (10) 177 (191, 176 (19), 151 (9), 102 (8), 88 (20) 177 (8). 176 (10). 151 (10) 103 (53) 202 (22), 201 (22), 165 (80)