Isomer effect of the production of negative ions from C6H4XY and C6H10X2 (X,Y = halogen)

The temperature dependence of the formation of negative ions from C6H4XY (X, Y = Cl, Br, I) and cyclo-C6H10X2 (X = Cl, Br) was studied using negative chemical ionization mass spectrometry. The heavier halide ion was mainly observed for C6H4XY The production rate of halide ions became greater in the order C6H4ClBr much less than C6H4ClI < C6H4BrI. The relative production rate of the major ions between isomers is related to the character of the substituted halogen atom in the system. The main observed ion was X- for C6H10X2. The production rate of halide ions increased in the order cyclo-cis-1,4-C6H10Cl2 < cyclo-trans-1,4-C6H10O2 similar to cyclo-trans-1,2-C6H10Cl2 much less than cyclo-trans-1,2-C6H10Br2. For cyclo-trans-1,2-C6H10Br2, not only Br-, but also Br-2(-), was observed. Four-center elimination with rotation of the C-Br bond seemed to occur when Br-2(-) was produced from cyclo-trans-1,2-C6H10Br2.