Energetic and vibrational assignment of tautomerizm of (Hydroxyphosphino)silanethione: A theoretical study

Abstract

The tautomerizm of (hydroxphosphino)silanethione molecule 1 were investigated by density function theory calculations. The potential energy surface, the global isomeric structures and the transition states of intramolecular proton transfer were calculated at B3LYP/6-31G(d) level of theory. The energy was further studied by a single point calculation by means of B3LYP/6-311++G(d,p) level. The potential energy surface was built-in of ten tautomers 2–11 along with ten transition states TS1–TS10 located for molecule 1. The global minimum at the B3LYP/6-31++G(d,p)//B3LYP/6-31G(d) levels of theory is 1. Tautomer 3 possessed the highest energy (136.06kJ/mol) above the global isomeric structure 1. The energies of the transition states reflect their different respective ring strains, TS2 with three-membered ring is possessed the highest energy (307.19kJ/mol) whereas the TS10 with four-membered ring had the lowest energy (107.17kJ/mol) among the transition states. The TS2 was clearly involved in the rate-determining step. The natural bond orbital (NBO) analysis reveals that the natural atomic charges are in conformity with bond lengths and electronic densities in the studied tautomers. The second order delocalization energies (E(2)) showed that there is a strong nS2→σP3–Si1∗ and nS2→σP3–Si1∗ interactions in the tautomers excluding structures 3 and 10. A strong nP3→σS2–Si1∗ interaction (240.10kJ/mol) is located for 3. Finally, strong nO4→σP3–S2∗ interaction (134.89kJ/mol) was found for 10 as expected since 10 is the only structure possessed a PS bond. The atoms in molecules (AIM) calculations of charge density at the bond critical point (BCP), (ρ(r) and ∇2ρ(r)) showed that for all SiS, SiP and SiH bonds were constructed by ionic or electrostatic interactions, whereas OH and SH bonds are maintained the covalent bond nature. The computed harmonic frequencies at B3LYP/6-31G(d) level showed that the values of the stretching frequencies of the most structures under consideration were in good agreement with the experimental values which have been reported for similar stretches.