Conformational isomerism

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

Determination of the geometry of deuterated tryptamine by rotationally resolved electronic spectroscopy

Abstract: The low and high resolution fluorescence excitation spectra of d3‐tryptamine have been observed in the environment of a cold, supersonic molecular beam. As in the case of h3‐tryptamine, six bands due to the origins of different conformers have been found in the low resolution spectrum of deuterated tryptamine. A previous paper reported that conformers labeled A and B and conformers labeled D and E of tryptamine have identical rotational structures. However, for deuterated tryptamine those conformers have distinguishable rotational structures. Analysis of the rotational structure in the high resolution electronic spectra of five of the bands was used to determine the geometries of the different conformers. Conformers A, B, and F have a gauche conformation with respect to the rotation about the Cα–Cβ bond while conformers D and E have an eclipsed conformation. The geometries of conformers A and B and conformers D and E differ only in the orientation of the amino group. In these structures the angles of the internal rotation of the amino group are 180°, 60°, 180°, 60°, and −60° for conformers A,B, and D–F, respectively. Feature C consists of two overlapped conformers, and it is suggested that these conformers have the amino group trans to the indole ring.

Effect of Double-Hyperconjugation on the Apparent Donor Ability of σ-Bonds: Insights from the Relative Stability of δ-Substituted Cyclohexyl Cations

Abstract: A combination of electronic, structural, and energetic analyses shows that a somewhat larger intrinsic donor ability of the C−H bonds compared to that of C−C bonds can be overshadowed by cooperative hyperconjugative interactions with participation of remote substituents (double hyperconjugation or through-bond interaction). The importance of double hyperconjugation was investigated computationally using two independent criteria: (a) relative total energies and geometries of two conformers (“hyperconjomers”) of δ-substituted cyclohexyl cations (b) and natural bond orbital (NBO) analysis of electronic structure and orbital interactions in these molecules. Both criteria clearly show that the apparent donor ability of C−C bonds can vary over a wide range, and the relative order of donor ability of C−H and C−C bonds can be easily inverted depending on molecular connectivity and environment. In general, relative donor abilities of σ bonds can be changed by their through-bond communication with remote substitue...

Cysteine conformations revisited

Abstract: Based on the B3LYP and MP2/aug-cc-pVDZ calculations, 51 cysteine conformers were found to be stable in the gas phase. The calculations were repeated for the most stable eight structures by using the aug-cc-pVTZ basis set. To estimate the influence of water on the cysteine conformation, the IEF-PCM/B3LYP/aug-cc-pVDZ calculations were carried out and showed 44 neutral and 12 zwitterion conformers to be stable in the water solution. The most stable cysteine structure in water appeared to be the zwitterionic conformer quite similar to the molecule observed in the crystal state.