A spin‐coupled investigation of the electrophilic addition of hydrochloric acid to ethylene

The gas-phase reaction of hydrochloric acid and ethylene to give chloroethane is investigated in the framework of spin-coupled (SC) theory, with emphasis on the widely accepted bimolecular mechanism. The transition-state structure and intrinsic reaction coordinate path are studied in detail. Our results indicate that the driving force in the reaction is the electrophilic attack of the hydrogen atom in HCl on one of the ethylenic carbons. There is little evidence supporting the occurrence of a four-membered transition state; rather, the spin-coupled results suggest that the breaking of the H-Cl bond occurs before the C-Cl bond formation. These findings are supported by the results from a topological analysis of the total electron density.