Ab initio molecular orbital and density functional studies on the ring-opening reaction of 2H-thiete

Electrocyclic ring opening (ERO) reaction of 2H-thiete has been carried out computationally in the gas phase and the ring opening barrier has been computed. When comparing the ERO reaction of 2H-thiete with the parent hydrocarbon (cyclobutene), the ring opening of cyclobutene is found to exhibit pericyclic behavior while 2H-thiete shows pseudopericyclic nature. Computation of the nucleus-independent chemical shift (NICS) of 2H-thiete adds evidence for pseudopericyclic behavior. Locking of the lone pair of electrons by hydrogen bonding was carried out to understand the extent of involvement of the lone pair of electrons during the course of the reaction. CR-CCSD(T)/6-311+G∗∗ computation was performed to assess the energies of the reactant, transition state and the product more accurately.