Reaction of halogenoacetylenes with sulphur nucleophiles studied by extended Hückel molecular orbital theory

Abstract

Extended HMO calculations have been carried out for the reactions of 1-halogeno-2-methyl- and 1-halogeno-2-phenylacetylenes with HS^–, in order to compare different positions of attack by the nucleophile (C-1, C-2, or halogen). Potential energy surfaces in the region of possible reaction intermediates have been obtained, and some definite minima have been found. Attack at C-1 appears to be favoured when halogen is F or Cl for both alkyl and aryl derivatives. Computations favour halogen attack in the case of iodo(phenyl)acetylene. Both kinds of attack seem possible for bromo(phenyl)acetylene. These results compare well with the outcome of experiments.