The Energy Difference between the Chair and Skew-Boat Forms of the 1,3-Dioxane Ring.

Pihlaja, Kalevi; Sandén, Roland; Krogh-Moe, J.; Schwieter, Ulrich; Paasiv́irta, Jaakko

doi:10.3891/acta.chem.scand.22-0716

Cited by 24 publications

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“…The experimental result based on NMR work (in benzene) shows that the axial conformation is favored over the equatorial by Δ G ° 298 = 0.89 kcal/mol. 13 Because the methyl ether of cyclohexanol has the methoxyl equatorial to the extent of about 0.5 kcal/mol experimentally, this is consistent with an “anomeric effect” of about 0.9 + 0.5 = 1.4 kcal/mol (in benzene). Previous work has suggested that solvation effects can play a significant role in stabilizing the equatorial form relative to the axial.…”

Section: ‐Methoxytetrahydropyranmentioning

confidence: 56%

“…The B value was not available when MM3 was developed, and the experimental value fit to now appears to have been 1–2 kcal too high. 13, 15, 19 The experimental value for Δ G ° favors the twist form for the tetramethyl compound by 1.8 kcal (with D = 4.8), and the MM3 and MM4 values are 0.56 and 1.53 kcal, respectively, for the gas phase (Table 8). We often make an approximate correction for solvation by dividing the electrostatic energy by the dielectric constant when the molecule is in a solvent.…”

Section: Substituted 13‐dioxanesmentioning

confidence: 97%

“…There are a number of experimental enthalpies for this value, which vary widely. 22, 23 A value of 5.88 kcal/mol was obtained from thermochemical data,13 6.0 kcal/mol from NMR,19 and from equilibration studies, a value of 7.4 kcal/mol has been reported. 15 Most studies refer to the 2,5‐twist form, but a study based on microcalorimetric measurements suggests that the gap between the chair and 1,4‐twist is 8.0 kcal/mol (Δ H ).…”

Section: 3‐dioxanementioning

confidence: 99%

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Alcohols, ethers, carbohydrates, and related compounds. II. The anomeric effect

et al. 2003

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The anomeric effect has been studied for a variety of compounds using the MM4 force field, and also using MP2/6-311++G(2d,2p) ab initio calculations and experimental data for reference purposes. Geometries and energies, including conformational, rotational barriers, and heats of formation were examined. Overall, the agreement of MM4 with the experimental and ab initio data is good, and significantly better than the agreement obtained with the MM3 force field. The anomeric effect is represented in MM4 by various explicit terms in the force constant matrix. The bond length changes are accounted for with torsion-stretch elements. The angle changes are accounted for with torsion-bend elements. The energies are taken into account with a number of torsional terms in the usual way. A torsion-torsion interaction is also of some importance. With all of these elements included in the calculation, the MM4 results now appear to be adequately accurate. The heats of formation were examined for a total of 12 anomeric compounds, and the experimental values were fit by MM4 with an RMS error of 0.42 kcal/mol.

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Section: ‐Methoxytetrahydropyranmentioning

confidence: 56%

Section: Substituted 13‐dioxanesmentioning

confidence: 97%

Section: 3‐dioxanementioning

confidence: 99%

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Alcohols, ethers, carbohydrates, and related compounds. II. The anomeric effect

et al. 2003

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“…Although the energy differences (Δ ) between the chair and the twist conformers of simple monoheterocyclohexanes seem not to be known, , it has been estimated experimentally from substituted 1,3-dioxanes that the twist conformer of 1,3-dioxane ( 2 ) is of higher energy relative to its chair conformer than that in cyclohexane ( 1 ). ,− It has also been estimated experimentally from substituted 1,3-dithianes that the Δ for 1,3-dithiane ( 3 ) is smaller than that for cyclohexane ( 1 ) and other saturated six-membered rings. ,,− …”

Section: Introductionmentioning

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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Non‐Chair Conformations of Six‐Membered Rings

Kellie

Riddell

1974

Topics in Stereochemistry

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The Energy Difference between the Chair and Skew-Boat Forms of the 1,3-Dioxane Ring.

Cited by 24 publications

References 0 publications

Alcohols, ethers, carbohydrates, and related compounds. II. The anomeric effect

Alcohols, ethers, carbohydrates, and related compounds. II. The anomeric effect

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

Non‐Chair Conformations of Six‐Membered Rings

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