Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones Evidence for

The conformational anal. of 2-phenylsulfinylcyclohexanone by ab initio d. functional calcns. is described. Six conformations corresponding to axial/equatorial isomers and rotation about the exocyclic C2,S bond in each of the RR or RS diastereomers were calcd. and the results were examd. in terms of...

Full description

Journal Title: Canadian Journal of Chemistry Vol. 84; no. 4; pp. 685 - 691
Authors: Walter W. Zajac, Melissa L. Trapp, John F. Wojcik, B. Mario Pinto
Format: Article
Published: 2006
Subjects:
Summary: The conformational anal. of 2-phenylsulfinylcyclohexanone by ab initio d. functional calcns. is described. Six conformations corresponding to axial/equatorial isomers and rotation about the exocyclic C2,S bond in each of the RR or RS diastereomers were calcd. and the results were examd. in terms of relative energies, electrostatic interactions, orbital interactions, and geometrical variations. The global min. conformation was the RS isomer that positioned the phenylsulfinyl moiety in an equatorial orientation and the sulfinyl oxygen in an anti orientation with respect to the carbonyl carbon atom. Of the other three low energy conformations, only one had a gauche arrangement of these atoms, and only in one of the four lower energy conformations was evidence found for a S-O(-)...C(+)-O electrostatic interaction. In contrast, the results were consistent with the operation of nS -> pi*C=O stabilizing orbital interactions. Further support for this hypothesis was obtained from the increased C=O bond lengths in these four conformations relative to the other conformations, and by the torsional angle distortion away from ideal geometry, presumably to maximize the stabilizing orbital interaction. We propose that this conformational preference is a manifestation of a generalized exo-anomeric effect. The longer C2,S bond in the axial isomers was also interpreted in terms of a stabilizing piC=O -> s*C-S interaction, analogous to an endo-anomeric interaction. Comparison of the computational results to available exptl. data on the conformational equil. of each diastereomer in soln. suggests which conformers are present in each of the equil. The available data for the solid state indicate that the RR and RS isomers both crystallize in high energy conformations, stabilized by intermol. interactions.
ISSN: 0008-4042
DOI: 10.1139/v06-040