Stereochemical course of a gas-phase electrophilic attack at saturated carbon. Reaction of meso-1,2-dichloro-1,2-difluoroethane with gaseous Broensted acids

The gas-phase electrophilic attack of He3HS ions from the @ decay of molecular tritium on nieso-1,2- dichloro-l,2-difluoroethanlee ads to the predominant formation of a tritiated product retaining the original configuration of the substrate, with a considerably smaller yield of the tritiated dl form. The effect of the substrate pressure on the meso/dl ratio and the use of radiolytically produced methanonium and ethyl ions as milder gasphase Bransted acids show that the minor yield of the dl form is likely to arise from a racemization process, rather than from a discrete mode of attack, leading to inversion. The conclusion that the gas-phase tritiodeprotonation proceeds with retention of the substrate configuration is compared with the theoretical predictions on the course of the SE2 substitution processes.