Conformational isomerism

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

Theoretical Prediction and the First IR Matrix Observation of Several L-Cysteine Molecule Conformers

Abstract: For the first time the argon-matrix low-temperature IR spectra of cysteine are recorded They reveal a quite complicated spectral pattern, which can also be reproduced in the N2 matrix Assignment of the observed spectra is undertaken on the basis of comparison of the experimental and calculated B3LYP/aug-cc-pVDZ anharmonic IR spectra The presence of at least three, and possibly even six or more, cysteine conformers with and without intramolecular hydrogen bonding is confirmed On the basis of the calculated vibrational circular dichroism spectra, we predict this technique to be more distinctive for conformers than IR absorption is

Intramolecular Hydrogen Bonds in Canonical 2‘-Deoxyribonucleotides: An Atoms in Molecules Study

Abstract: The molecular structure and relative stability of different conformers of isolated canonical 2'-deoxyribonucleotides thymidine-5'-phosphate (pdT), 2-deoxycytidine-5'-phosphate (pdC), 2-deoxyadenosine-5'-phosphate (pdA), and 2'-deoxyguanosine-5'-phosphate (pdG) were calculated using the B3LYP/6-31++G(d,p) level of theory The results of the calculations reveal that, for all nucleotides except pdG, conformers with a syn orientation of the base do not correspond to a minimum on the potential energy surface In the case of pdA and pdC, conformers with an orthogonal orientation of the nucleobase are located instead, north/syn conformers These conformers as well as syn conformers of pdG are stabilized by intramolecular N-HO hydrogen bonds Analysis of the electron density distribution within the atoms in molecules theory reveals the presence of numerous C-HO hydrogen bonds in the nucleotides However, a more detailed consideration of the properties of these bonds demonstrates that many of them should be considered as strong attractive electrostatic interactions rather than true hydrogen bonds True hydrogen bonds are represented mainly by C6/ C8-HO5'/O-P in anti conformers and the N-HO-P bonds in syn conformers It is demonstrated that the values of ellipticity of the electron density at the bond critical point (BCP) and the distance between BCP and ring critical point are the most reliable indicators for determining the true intramolecular hydrogen bonds

Rotational Spectra of Seven Conformational Isomers of 1-Hexene

Abstract: The rotational spectra of 7 of the expected 13 conformational isomers of 1-hexene have been measured and assigned at a rotational temperature of <2 K using a pulsed-molecular-beam Fourier transform microwave spectrometer. The rotational assignments were guided by predictions from the MM3 molecular mechanics force field of Allinger et al. and by ab initio electronic-structure calculations (MP2/6-31G*). Six of the seven observed conformers have C1 symmetry, as verified by the observation of a-, b-, and c-type electric-dipole transitions. The remaining conformer has Cs symmetry, consistent with its small inertial defect, Δ ≡ Icc − Ibb − Iaa = −12.65 uA2, and the observation of only a and b-type transitions. Here, Iαα is the moment of inertia of the conformer about its α-principal axis. The inertial defects determined for the seven conformers range from −12.65 to −51.29 uA2. Both the molecular mechanics and ab initio calculations indicate the observed conformers are associated with the seven lowest-energy con...

Discrimination of Rotamers of Aryl Alcohol Homologues by Infrared−Ultraviolet Double-Resonance Spectroscopy in a Supersonic Jet

Abstract: Infrared−ultraviolet double-resonance spectroscopy has been applied to discriminate rotamers of jet-cooled aryl alcohol homologues, φ-(CH2)nOH, where φ represents phenyl group and n = 1, 2, and 3 correspond to benzyl, phenethyl, and 3-phenylpropyl alcohols, respectively. Experimental results indicate that different OH stretching frequencies are associated with different rotamers and that the ability of intramolecular hydrogen bonding with the benzene π-electron decreases with an increase in alkyl chain length. In each aryl alcohol, the most prominent species in jets corresponds to the non-hydrogen-bonded rotamer having higher OH stretching frequency.