Computational study of the conformational interconversion of 5,5‐dimethyl‐1,2,3‐trithiacyclohexane (5,5‐dimethyl‐1,2,3‐trithiane)

Abstract

AbstractAb initio molecular orbital theory and density functional theory (DFT) with the 6‐31G(d), 6‐31G(d,p), 6‐31+G(d,p), and 6‐311+G(d,p) basis sets have been used to study the mechanism of conformational interconversion of 5,5‐dimethyl‐1,2,3‐trithiacyclohexane (5,5‐dimethyl‐1,2,3‐trithiane). The relative energies, enthalpies, entropies, free energies, and structural parameters of the chair, 1,4‐twist, and 2,5‐twist conformers, the 1,4‐boat transition state, and the 2,5‐boat transition state were calculated. B3LYP/6‐31+G(d,p) calculated the chair conformer of 5,5‐dimethyl‐1,2,3‐trithiane to be 8.38 and 8.72 kcal/mol, respectively, lower in energy than the 1,4‐twist and 2,5‐twist conformers. The energy differences (ΔE) between the chair conformer of 5,5‐dimethyl‐1,2,3‐trithiane and the 1,4‐boat transition state and the 2,5‐boat transition state were 8.95 and 11.46 kcal/mol, respectively. Intrinsic reaction coordinate [IRC, minimum energy path (MEP)] calculations were used to connect the transition state between the chair conformer and 2,5‐twist conformer. B3LYP/6‐31+G(d,p) calculated energy differences (ΔE) between the chair conformer and the transition state [TS‐1]‡ connecting the chair and 2,5‐twist conformers to be 14.23 kcal/mol. In the chair, 1,4‐twist, and 2,5‐twist conformers, the C4Heq bond is slightly longer than the C4Hax bond. The C5C8eq bond is longer than the C5C7ax bond in the chair and 1,4‐twist conformers. In the 1,4‐twist conformer, the S1S2 bond is longer than the S3S3 bond and the S1C6 bond is longer than the S3C4 bond. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004