Conformational isomerism

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

Conformers of nonionized proline. matrix-isolation infrared and post-hartree - fock ab initio study

Abstract: Matrix-isolation IR spectroscopy and ab initio calculations performed at the DFT, MP2, MP4, and CCSD(T) levels of theory were employed to investigate the conformational topology of the nonionized amino acid proline and its deuterated derivative, N,O-dideuteroproline (proline-d2). In the calculations, equilibrium structures of 15 low-energy proline conformers were obtained using the DFT/B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ methods. The harmonic frequencies and IR intensities of the conformers were calculated for the DFT geometries, and these data was used to account for the zero-point vibration energy correction and to assist the analysis of the experimental matrix-isolation IR spectra. Two proline conformers were found to be present in the Ar matrix. They are the lowest energy conformer with a N···HO H bond (conformer IIa) and the second conformer with a NH···OC H bond (conformer Ia). We found that the DFT/B3LYP and MP2 methods are not capable of predicting the relative energies of the proline conformers...

Conformational Choice, Hydrogen Bonding, and Rotation of the S1 ← S0 Electronic Transition Moment in 2-Phenylethyl Alcohol, 2-Phenylethylamine, and Their Water Clusters

Abstract: Laser-induced fluorescence and one- and two-color, mass- selected R2PI excitation spectra of the S1 ← S0 electronic transitions in 2-phenylethyl alcohol and 2-phenylethylamine have been recorded in a jet-cooled environment. Five conformers of 2-phenylethyl alcohol and four of 2-phenylethylamine have been identified, together with a number of 1:1 hydrated water clusters. The fifth origin band in the excitation spectrum of 2-phenylethylamine has been reassigned to a water cluster, primarily on the basis of its ion fragmentation pattern. Analysis of their partially resolved rotational band contours has been aided by ab initio molecular orbital calculations, conducted at levels of theory ranging from MP2/3-21G* to MP2/6-311G** for the ground state and CIS/6-311G** for the first electronically excited singlet state. The reliability of the CIS method has also been tested through benchmark calculations, including computations on a related, experimentally known conformational system, methyl 3-hydroxybenzoate. 2-P...

Directional electron transfer: conformational interconversions and their effects on observed electron-transfer rate constants

Abstract: The interaction between conformation changes and electron-transfer rates is considered for systems containing two redox centers. The effect of conformation changes on the free-energy barrier to intramolecular electron transfer is examined. Unstable conformers R* of the reactant (or P* of the product) that are either more (low-{lambda} intermediates) or less (high-{lambda} intermediates) redox-active than the stable reactant R (or product P) are considered. The relative energies of the conformers determine whether the observed electron-transfer reaction proceeds by a two-step mechanism involving the intermediate formation of an unstable conformer or by a direct (concerted) reaction involving only the stable reactant and product. The present analysis generates a set of equations that indicate when the two-step or the direct mechanism is energetically favored. Only when the two-step mechanisms are favored is gating or conformational control possible.