Influence of nonbonded interactions in the kinetics of formation of chalcogenol esters from chalcogenoacetylenes

The influence of nonbonded interactions in the kinetics of formation of chalcogenol (thiol and selenol) esters from chalcogenoacetylenes was studied by molecular modeling. Using semiempirical and density functional theory methods it was possible to explain the differences between the reaction rates for the analogous sulfur and selenium chalcogenoacetylenes as well as evaluate the structural and electronic effects (nonbonded interactions) on the formation of the esters. The differences in the reaction rates can be explained in terms of the carbocation stabilization by the chalcogen atom. It is proposed that these differences are due to the differences in the intensity of the dominant interaction π /n Y between the nonbonding orbitals of sulfur and selenium with the vacant orbital of carbon in the cationic transition state.