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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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TL;DR: It is concluded that crystal packing effects rarely have a strong systematic effect on molecular conformations, and the conformational distribution of a molecular substructure in a series of related crystal structures is likely to be a good guide to the corresponding gas-phase potential energy surface.
Abstract: The conformational preferences of 12 molecular substructures in the crystalline state have been determined and compared with those predicted for relevant model compounds by ab initio molecular orbital calculations. Least-squares regression shows that there is a statistically significant correlation between the crystal-structure conformer distributions and the calculated potential-energy differences, even though the calculations relate to a gas-phase environment. Torsion angles associated with high strain energy (>1 kcal mol-1) appear to be very unusual in crystal structures and, in general, high-energy conformers are underrepresented in crystal structures compared with a gas-phase, room-temperature Boltzmann distribution. It is concluded that crystal packing effects rarely have a strong systematic effect on molecular conformations. Therefore, the conformational distribution of a molecular substructure in a series of related crystal structures is likely to be a good guide to the corresponding gas-phase potential energy surface.

97 citations

Journal ArticleDOI
TL;DR: In this article, a vibrational assignment for both s-cis and s-trans conformers of pyrrole-2-carboxylic acid conformers is proposed.
Abstract: The infrared and Raman spectroscopic study of pyrrole-2-carboxylic acid (PCA) confirms the formation of the cyclic acid dimer species in the solid state. The molecular structure, vibrational frequencies, and binding energies of cyclic dimers have been also examined using the density functional theory (DFT) at the B3LYP/6-311+G(d) level. In addition, a complete vibrational assignment is proposed for the both s-cis and s-trans PCA conformers. The vibrational assignments are supported by normal coordinate calculations utilizing force constants predicted using the DFT method. The “atoms in molecules” theory of Bader is also used to characterize hydrogen bonds.

97 citations

Journal ArticleDOI
TL;DR: A strategy to design face discriminated glycosyl donors that exist predominantly in only one family of conformers is proposed based on observations of high beta-stereoselectivity of mannopyranosyl donors and high alpha-stirring of glucopyranoyl donors with the 4,6-O-benzylidene protecting groups.

96 citations

Journal ArticleDOI
TL;DR: In this paper, the free energy of activation of hindered rotation was estimated as 13.5 kcal mol−1 for lupeol (1a) and two derivatives where the C-30 methyl group is replaced by CH2OH (1b) and HC O (1c).
Abstract: Complete 1H and 13C spectral assignments are reported for lupeol (1a) and two derivatives where the C-30 methyl group is replaced by CH2OH (1b) and HC O (1c). Compound 1c shows conformationally dependent substituent effects on 1H chemical shifts. It also shows line broadening of some 13C signals at 25 °C, suggesting hindered rotation of the side-chain group. This is confirmed by low-temperature spectra which show splitting of broadened peaks into pairs in a ca 2 : 1 area ratio. The free energy of activation of hindered rotation is estimated as 13.5 kcal mol−1. By contrast, 1a shows no evidence of hindered rotation down to −40 °C although NOE data suggest the presence of two conformers. Spartan molecular mechanics calculations confirm the presence of two stable conformers for 1a and 1c but overestimate the rotational barrier in 1a. The additional barrier in 1c probably reflects loss of conjugative stabilization during rotation. Copyright © 2000 John Wiley & Sons, Ltd.

96 citations

Journal ArticleDOI
TL;DR: This work demonstrates the first UHV-TERS on Cu(111) and shows TERS can unambiguously distinguish the conformational differences between neighboring molecules with Ångstrom-scale spatial resolution, thereby establishing it as a leading method for the study of metal-adsorbate interactions.
Abstract: Tip-enhanced Raman spectroscopy (TERS) combines the ability of scanning probe microscopy (SPM) to resolve atomic-scale surface features with the single-molecule chemical sensitivity of surface-enhanced Raman spectroscopy (SERS) Here, we report additional insights into the nature of the conformational dynamics of a free-base porphyrin at room temperature adsorbed on a metal surface We have interrogated the conformational switch between two metastable surface-mediated isomers of meso-tetrakis(3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP) on a Cu(111) surface At room temperature, the barrier between the porphyrin ring buckled up/down conformations of the H2TBPP-Cu(111) system is easily overcome, and a 26 A lateral resolution by simultaneous TERS and STM analysis is achieved under ultrahigh vacuum (UHV) conditions This work demonstrates the first UHV-TERS on Cu(111) and shows TERS can unambiguously distinguish the conformational differences between neighboring molecules with Angstrom-scale spatial resolu

96 citations


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