Mass spectral study of substituted methyl (E)-and (Z)-cinnamates under 1,2-dibromoethane chemical ionization

Dibromoethane chemical ionization mass spectra of ten pairs of methyl (E)- and (Z)-cinnamates were studied. C₂H₄Br⁺ ion forms stable adducts with E-isomers and the adducts of Z-isomers show preferential loss of methanol. The observed results suggest that the probability of ring alkylation is greater than with the carbonyl group.