The molecular conformation and dipole moment of 1,4-thioxane from the microwave spectrum

Kitchin, R.W.; Avirah, T. K.; Malloy, Thomas B.; Cook, Robert L.

doi:10.1016/0022-2860(75)87010-4

Cited by 12 publications

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“…All levels of theory calculated the S1−C2 bond length to be shorter than the S1−C6 bond length in the chair conformer ( 3 ). The C−S bond lengths have been determined experimentally in tetrahydro-2 H -thiopyran ( C s symmetry, ED 1.832 Å, MW 1.811 Å), 1,4-dithiacyclohexane (1,4-dithiane, C 2 h symmetry, ED 1.81 Å, X-ray 1.81), 4-oxa-1-thiacyclohexane (1,4-oxathiane, 1,4-thioxane, ED 1.826 Å, , MW 1.824 Å), and 1,4-thioselenane (1.81 Å) . Thus, the experimental and the HF, MP2, B3P86/6-31G(d), and B3PW91/6-31G(d) calculated S1−C2 and C2−S3 bond lengths in the chair conformer ( 3 ) of 1,3-dithiane are similar to the observed C−S bond lengths in tetrahydro-2 H -thiopyran, 1,4-dithiane, and 1,4-thioselenane.…”

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confidence: 99%

A Computational Study of Conformations and Conformers of 1,3-Dithiane (1,3-Dithiacyclohexane)

Freeman

2003

J. Phys. Chem. A

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Ab initio molecular orbital theory with the 6-31G(d), 6-31G(d,p), 6-31+G(d), 6-31+G(d,p), and 6-311+G(d,p) basis sets and density functional theory (BLYP, BP86) including the hybrid density functionals B3LYP, B3P86, and B3PW91 have been used to investigate stereoelectronic hyperconjugative interactions and relative energies of the chair, 1,4-twist, and 2,5-twist conformers of 1,3-dithiane (1,3-dithiacyclohexane). The HF/6-31G(d) energy difference (ΔE) between the chair conformer and the 1,4-boat transition state was 5.53 kcal/mol, and the B3LYP/6-311+G(d,p) energy difference between the chair conformer and the 2,5-boat transition state was 5.42 kcal/mol. Intrinsic reaction coordinate (IRC, minimum energy path) calculations have been used to connect the enantiomers of the 1,4-twist conformer via the 2,5-boat transition state. The B3LYP/6-311+G(d,p) calculated energy difference between the 1,4-twist conformer and the 2,5-boat transition state was 0.80 kcal/mol. The HF/6-31G(d) energy difference (ΔE) between the chair conformer and the 2,5-twist conformer was 4.24 kcal/mol, and the 2,5-twist conformer was 0.48 kcal/mol lower in energy than the 1,4-twist conformer. The chair−1,4-twist free energy difference (Δ ) is 4.42 kcal/mol, and the chair−2,5-twist Δ is 4.27 kcal/mol. IRC calculations connected the chair conformer and 2,5-twist conformer on the potential energy surface by a path that passes through the transition state [TS-1]‡ between them. IRC reaction path computations also connected transition state [TS-2]‡ to the chair conformer and the 1,4-twist conformer. The transition state [TS-2]‡ between the chair and the 1,4-twist conformers is 9.89 kcal/mol higher in energy than the chair conformer, and the transition state [TS-1]‡ between the chair and the 2,5-twist conformers is 10.44 kcal/mol higher in energy than the chair conformer. The C2−Hax, C4−Hax, and C6−Hax bond lengths are longer than the corresponding C−Heq bond lengths in the chair conformer (LPS → σ*C - Hax, σ C - Hax → σ* C - Hax). In contrast, the C5−Heq bond in the chair conformer is longer than the C5−Hax bond (σS - C → σ*C5 - Heq, W effect, or homoanomeric LPS → σ*C5 - Heq). The importance of geometrical considerations in stereoelectronic hyperconjugative interactions is shown in the twist conformers and transition states of 1,3-dithiane. Unlike the chair conformer, in the 2,5-twist conformer, the respective C−H bond lengths at each carbon are equal and the C2−Hiso bond lengths are shorter than the C5−Hiso bond lengths. In the 1,4-twist conformer, the respective C−H bond lengths at C2, C4, and C6 are equal and the C5−Heq bond length is longer than the C5−Hax bond length (σS - C → σ*C5 - Heq, W effect, or homoanomeric LPS → σ*C5 - Heq).

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