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Conformational isomerism

About: Conformational isomerism is a research topic. Over the lifetime, 11563 publications have been published within this topic receiving 199312 citations.


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Journal ArticleDOI
TL;DR: In this article, the conformational energy map for the rotamers of dimethoxymethane has been calculated using both the 3-21G and 6-31G* basis sets with complete geometry optimization in each case.
Abstract: The conformational energy map for the rotamers of dimethoxymethane has been calculated using both the 3-21G and 6-31G* basis sets with complete geometry optimization in each case. Higher level calculations including electron correlation also have been performed on selected rotamers. At larger torsional angles, the map has approximate 4-fold symmetry, and this symmetry may be used to quantify the difference in the interactions in the (+sc, {minus}sc) and (+sc, +sc) regions. Large changes in bond angles were found, and the dipole moment also changed considerably on C-O bond rotation. Calculations on equatorial and axial 2-methoxytetrahydropyran show that the axial form is favored by 1.33 kcal/mol, in fair agreement with experiment. Calculations also were carried out on the two lowest energy forms of 1,1-dimethoxyethane and on five forms of methyl propyl ether. Consideration of all these data indicates that the anomeric stabilization in dimethoxymethane is much greater than in sterically more congested systems, but the stabilization of 1,1-dimethoxyethane is similar to that of 2-methoxytetrahydropyran and other acetals.

131 citations

Journal ArticleDOI
TL;DR: In this paper, an analysis of the rotamer distribution in the hydroxymethyl side chain showed that the trans, gauche conformer is strongly disfavored in aqueous solution.
Abstract: The calculated free energy difference is the result of near cancelation of two larger, statistically significant contributions, i.e., an intramolecular electrostatic term favoring the α anomer and an intermolecular solute-solvent interaction term favoring the β anomer. This result supports the conjecture that solvation stabilizes the β anomer in water. There is a large difference in the intramolecular contribution to the anomeric equilibrium calculated in solution from the free energy simulation and the gas-phase minimum; this suggests that conformational averaging, modulated by the solvent, is significant even for the internal terms. An examination of the rotamer distribution in the hydroxymethyl side chain shows that the trans, gauche conformer is strongly disfavored in aqueous solution, in accord with experiment

131 citations

Journal ArticleDOI
TL;DR: In this paper, the enthalpy difference between the more stable cis conformer and the high-energy gauche rotamer has been determined to range from 60 ± 8 cm-1 (718 ± 96 J/mol) in liquid xenon to 81 ± 1 cm -1 (969 ± 12 J/m) in Liquid argon.
Abstract: The infrared spectra (3500−400 cm-1) of 3-fluoropropene (allyl fluoride), CH2C(H)CH2F, dissolved in liquid argon, krypton, and xenon have been recorded at various temperatures ranging from −180 to −65 °C. From these studies, the enthalpy difference between the more stable cis conformer and the high-energy gauche rotamer has been determined to range from 60 ± 8 cm-1 (718 ± 96 J/mol) in liquid xenon to 81 ± 1 cm-1 (969 ± 12 J/mol) in liquid argon. These values have been extrapolated utilizing a linear relationship between the Kirkwood function of the solvent and the enthalpy differences in the solvents to give a value of 130 ± 25 cm-1 (1.56 ± 0.30 kJ/mol) for the vapor. From the experimental enthalpy value, the gauche dihedral angle, torsional transitions for both rotamers, and better structural parameters, the potential function governing the conformational interchange has been recalculated. Ab initio calculations utilizing the 6-31G(d,p) and 6-311G(d,p) basis sets with electron correlation at the MP2 leve...

131 citations

Journal ArticleDOI
TL;DR: These calculations indicate that the enthalpic and entropic contributions to the Gibbs free energy are important for an accurate determination of the conformational and energetic preferences of glycerol.
Abstract: The 126 possible conformations of 1,2,3-propanetriol (glycerol) have been studied by ab initio molecular orbital and density functional theory calculations in the gas and aqueous phases at multiple levels of theory and basis sets. The partial potential energy surface for glycerol as well as an analysis of the conformational properties and hydrogen-bonding trends in both phases have been obtained. In the gas phase at the G2(MP2) and CBS-QB3 levels of theory, the important, low-energy conformers are structures 100 and 95. In the aqueous phase at the SM5.42/HF/6-31G* level of theory, the lowest energy conformers are structures 95 and 46. Boltzmann distributions have been determined from these high-level calculations, and good agreement is observed when these distributions are compared to the available experimental data. These calculations indicate that the enthalpic and entropic contributions to the Gibbs free energy are important for an accurate determination of the conformational and energetic preferences of glycerol. Different levels of theory and basis sets were used in order to understand the effects of nonbonded interactions (i.e., intramolecular hydrogen bonding). The efficiency of basis set and level of theory in dealing with the issue of intramolecular hydrogen bonding and reproducing the correct energetic and geometrical trends is discussed, especially with relevance to practical computational methods for larger polyhydroxylated compounds, such as oligosaccharides.

129 citations

Journal ArticleDOI
TL;DR: In this article, the authors determined the bond distances (rg) and angles (rα) in N-methylacetamide by gas electron diffraction, and the two methyl groups are in the trans conformation about the N-C (carbonyl) bond, no other conformer being observed.
Abstract: The bond distances (rg) and angles (rα) in N-methylacetamide have been determined by gas electron diffraction as follows: C–C=1.520±0.005 A, N–C (methyl)=1.469±0.006 A, N–C (carbonyl)=1.386±0.004 A C=O=1.225±0.003 A, C–H (average)=1.107±0.005 A, ∠N–C=O=121.8±0.4°, ∠C–N–C=119.7±O.8°, ∠C–C–N=114.1±1.5°, ∠H–C–H(average)=110.4±2° and ∠H–N–C(carbonyl)=110±5°. In comparison with the molecular structure in the crystal, the N–C(carbonyl) bond is about 0.10 A longer, whereas the C–C and C=O bonds are about 0.02 and 0.01 A shorter, respectively. The two methyl groups are in the trans conformation about the N–C (carbonyl) bond, no other conformer being observed.

129 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023303
2022618
2021217
2020219
2019228
2018268