scispace - formally typeset
Search or ask a question
Topic

Conformational isomerism

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


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the rotational spectrum of a particular conformer of glycine in the vapor phase (labeled conformer) was analyzed and the excellent agreement between experiment and theory was discussed.
Abstract: More sensitive observations on the vapor of glycine, the smallest amino acid, have been made in the millimeter region. This work has led to the identification of a second conformer in the gas phase. This conformer has the amino hydrogens hydrogen bonded to the carbonyl oxygen and the hydroxyl hydrogen in the normal cis configuration with respect to the carbonyl group. This new conformer is ~490 (150) cm-I lower in energy than the conformer originally reported. Its spectrum is weaker due to the smaller dipole moment (wa E 1.00 (15) D). The distortion fit of 37 transitions yield A" = 10341.76 (17) MHz, B" = 3876.195 (9) MHz, and C" = 2912.361 (10) MHz for the ground state. The excellent agreement between experiment and theory is discussed. Introduction moments, their rotational sDectra might indeed be weaker than In our previous paper on the millimeter wave spectrum of glycine we reported the rotational spectrum of a particular con- former of glycine in the vapor phase (labeled conformer

266 citations

Journal ArticleDOI
TL;DR: The conformation of the 7-membered hydrogen-bonded ring of the dipeptides has been elucidated and an empirically found stereochemical dependence of the constant 3 J NHCH upon the dihedral angle θ of the fragment has served as basis for discussing the possible conformations of the extended form of the Dipeptide molecules in polar solvents.

261 citations

Journal ArticleDOI
TL;DR: An empirical scale for the loss of side-chain conformational entropy during protein folding is obtained and the stability of site-directed mutations is discussed in terms of conformational Entropy.

259 citations

Journal ArticleDOI
TL;DR: In this paper, a steady-state and time-resolved emission spectroscopy at various temperatures and by semi-empirical quantum chemical methods has been used to study an excited-state intramolecular proton transfer (ESIPT) process in 2-(2'-hydroxyphenyl) benzimidazole and -benzoxazole (HPBI and HBO, respectively).
Abstract: An excited-state intramolecular proton transfer (ESIPT) process in 2-(2’-hydroxyphenyl) benzimidazole and -benzoxazole (HPBI and HBO, respectively) has been studied using steady-state and time-resolved emission spectroscopy at various temperatures and by semiempirical quantum chemical methods. For both of them two distinct ground-state rotamers I and I1 respectively responsible for the “normal” and the “tautomer” emission have been detected. In hydrocarbon solvents at room temperatureand at 77 K the tautomer emission predominates over the normal emission for both HPBI and HBO. This indicates that rotamer 11, responsible for the tautomer emission, is intrinsically stabler than rotamer I, which causes the normal emission. In alcoholic glass at 77 K for HPBI a dramatic enhancement of the normal emission is observed. It is suggested that due to the increased solvation, the more polar rotamer I becomes stabler than I1 for HPBI in alcohol and the substantial temperature variation is due to the change in the population of the two rotamers with temperature. From the detailed temperature variation in alcoholic medium the ground-state energy difference between rotamers I and I1 is determined. In dioxane-water mixtures it is observed that with the addition of water the quantum yield of the normal emission increases, which is ascribed to the inhibition of the ESIPT process due to the formation of an intermolecular hydrogen bond involving water. CNDO/S-CI calculations were performed optimizing thegroundstate geometry by the AM1 method. Details of the energy, dipole moment, and charge distribution of the rotamers in the ground state (SO) and the first excited singlet state (SI) and the barrier for the interconversion of I and I1 in SO, SI, and first excited triplet state are discussed. The calculation indicates that the barrier for the interconversion of the two rotamers is too high in the excited state (SI and TI) for free interconversion.

256 citations

Journal ArticleDOI
TL;DR: In this article, three conformers of cinchonidine are shown to be substantially populated at room temperature, Closed(1), Closed(2), and Open(3), with the latter being the most stable in apolar solvents.
Abstract: The conformation of cinchonidine in solution has been investigated by NMR techniques as well as theoretically. Three conformers of cinchonidine are shown to be substantially populated at room temperature, Closed(1), Closed(2), and Open(3), with the latter being the most stable in apolar solvents. The stability of the closed conformers relative to that of Open(3), however, increases with solvent polarity. In polar solvents the three conformers have similar energy. The relationship between relative energies and the dielectric constant of the solvent is not linear but resembles the form of an Onsager function. Ab initio and density functional reaction field calculations using cavity shapes determined by an isodensity surface are in good agreement with experiment for solvents which do not show strong specific interaction with cinchonidine. The role of the conformational behavior of cinchonidine is illustrated using the example of the platinum-catalyzed enantioselective hydrogenation of ketopantolactone in dif...

256 citations


Network Information
Related Topics (5)
Molecule
52.4K papers, 1.2M citations
93% related
Hydrogen bond
57.7K papers, 1.3M citations
92% related
Ab initio
57.3K papers, 1.6M citations
91% related
Nuclear magnetic resonance spectroscopy
42.6K papers, 1M citations
91% related
Ligand
67.7K papers, 1.3M citations
90% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023303
2022618
2021217
2020219
2019228
2018268