Abstract
The insertion of 1CH2, 1CHF, 1CF2,1CHCl, and 1CCl2 into primary and secondary polar S‒H bonds of methanethiol, ethanethiol, 1-propanethiol, and 2-propanethiol have been investigated at HF (Hartree–Fock), MP2 (Møller–Plesset Perturbation Theory), and DFT (density functional theory) levels using 6-31G (d, p) basis set. The insertions follow a two-step mechanism. The potential energy surface exploration identifies ylide-like structures undergoing the 1,2-sigmatropic hydrogen shift concertedly giving the thioether product. But 1CF2 forms weak complexes involving 1,2-hydrogen shift. The barrier height in the concerted mechanism varies with the type of carbene moiety and S‒H bond. The initial interaction seems to be a function of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies of thiols and carbenes, respectively. The natural bond orbital charge analysis showing a net charge flow from the substrate thiol to the reagent carbene at the transition states corroborates this fact.
GRAPHICAL ABSTRACT
Acknowledgments
The author is thankful to Prof. H. Saleem, Department of Physics, Annamalai University, Chidambaram, India, for allowing to do the calculations using Gaussian 03W program.