Anti-Markovnikov selectivity in the addition of thermal chlorine to CH{sub 2}=CHBr and CF{sub 2}=CFBr

The addition of thermal chlorine atoms to CH{sub 2}=CHBr and CF{sub 2}=CFBr has been studied at 23{degrees}C from 500 to 3000 torr using {sup 38}Cl from the neutron irradiation of CF{sub 3}Cl as well as thermal {sup 35,37}Cl from the photolysis of COCl{sub 2}. For CH{sub 2}=CHBr, only a slight {open_quotes}anti-Markovnikov{close_quotes} preference for addition to CH{sub 2} vs. CHBr of 1,4 was found, along with a 1,2-bromine migration in the stabilized CH{sub 2}CHBrCl radical. For CF{sub 2}=CFBr, the {open_quotes}anti-Markovnikov{close_quotes} preferences for addition to CF{sub 2} vs. CFBr was found to be 3.0. Mass spectroscopy after radical termination with D{sub 2}S was used with the stable isotopes and CH{sub 2}=CHBr, while radio gas chromatography was applied for {sup 38}Cl analysis. An {open_quotes}anti-Markovnikov{close_quotes} preference is often accompanied by appreciable initial yields of the less-favored radical.