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Molecular modeling studies of novel heteroarotinoids
Author(s) -
Welsh William J.,
Cody Vivian
Publication year - 1990
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540110412
Subject(s) - chemistry , dihedral angle , crystal structure , steric effects , crystallography , bond length , molecular geometry , crystal (programming language) , force field (fiction) , molecular orbital , perpendicular , thio , computational chemistry , potential energy , molecule , stereochemistry , hydrogen bond , geometry , atomic physics , physics , mathematics , organic chemistry , quantum mechanics , computer science , programming language
Abstract The molecular structure and conformational properties of structurally related oxo and thio heteroarotinoids have been calculated by employing AM1 molecular orbital and both MM2P and Chem‐X “optimize” molecular mechanics methods, and the results have been compared with crystal structure data. For the cis and trans oxo heteroarotinoids, MM2P gives values of the bridge torsion angles ϕ 1 and ϕ 2 in closest agreement with the crystal structure, and all three computational methods yield values of ϕ 1 and ϕ 2 within about 10° of that found in the crystal structures. All three computational methods locate a minimum‐energy conformation for the trans isomer corresponding to the two bridged aryl rings being mutually perpendicular, in agreement with the crystal structure and similar to that found for the structurally analogous trans ‐stilbene. The calculated heteroring geometries also reproduce the twist‐sofa conformation observed for the crystal structure. Calculated conformational energies versus ϕ 1 and ϕ 2 indicate broad energy wells about the minimum‐energy conformation with barriers to rotation at the planar and perpendicular conformations, and with higher barriers found for the more sterically congested cis isomer. The corresponding cis and trans thio heteroarotinoids exhibit conformational properties similar to their oxo analogues. Both AM1 and MM2P fare poorly in reproducing the crystal structure values of the sulfur‐containing bond lengths and bond angles. The C‐S bonds found in these thio heteroarotinoids may possess more double‐bond character than accounted for in the calculations. Also, the results suggest that the MM2P sulfur‐related force‐field parameters adopted for these calculations may require further refinement.