This work describes a theoretical approach to the substitution reaction mechanism involving the conversion of cholesterol to cholesteryl chloride. Two chlorosulfite ester molecules were formed as intermediates. An iso-steroid was found as the transition state. The final product was cholesteryl chloride and the side products were HCl and SO2. Calculations were carried out at high level Hartree-Fock theory, using the 6-31G* basis set. From the electronic structure of the reactants, the most important physicochemical properties involved in the reaction pathway were used. Thus, to determine the participation of each molecule and to explain the mechanism of reaction; the total energy, HOMO and LUMO, atomic orbital contribution to frontier orbitals formation, electrostatic potentials, atomic charges, hardness and dipole moment were used. Characterization of intermediates and transition state was supported by their respective energy minima, fundamental frequencies and equilibrium geometry.
