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Computational study of the conformational interconversion of 5,5‐dimethyl‐1,2,3‐trithiacyclohexane (5,5‐dimethyl‐1,2,3‐trithiane)
Author(s) -
Freeman Fillmore,
Cha Chansa
Publication year - 2003
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.10739
Subject(s) - conformational isomerism , chemistry , ab initio , twist , ground state , crystallography , computational chemistry , molecule , physics , atomic physics , geometry , organic chemistry , mathematics
Abstract Ab 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 (Δ E ) 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 (Δ E ) 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 C4Heq bond is slightly longer than the C4Hax bond. The C5C8eq bond is longer than the C5C7ax bond in the chair and 1,4‐twist conformers. In the 1,4‐twist conformer, the S1S2 bond is longer than the S3S3 bond and the S1C6 bond is longer than the S3C4 bond. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004