Abstract: Kinetic studies of the reactions of substituted aryl (bromodichloromethy1) mercury compounds, p-ZCG-H4HgCCIJBr (Z= H, C1, F, Me, MeO), with Me2C= CMeEt in benzene solution at 39.0" showed that the rate of CCI, extrusion from these mercurials differs only slightly as a function of Z. This insensitivity to electronic factors is taken as evidence in support of a concerted CC1, extrusion process proceeding ria the cyclic transition state I. A ...