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Cumulative anomeric effect: a theoretical and X-ray diffraction study of orthocarbonates

Narasimhamurthy, N and Manohar, H and Samuelson, Ashoka G and Chandrasekhar, Jayaraman (1990) Cumulative anomeric effect: a theoretical and X-ray diffraction study of orthocarbonates. In: Journal of American Chemical Society, 112 (8). pp. 2937-2941.

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The combined effect of six anomeric pair interactions at a single carbon atom has been examined by X-ray diffraction and molecular mechanics. MM2 calculations on $C(OR)_4 (R = H, Me, Ph)$ indicate two closely spaced minima with $S_4$ and $D_{2d}$ symmetry. An interesting low-energy pathway resembling a three-dimensional domino has been computed for the interconversion of the $S_4$ conformer to the $D_{2d}$ form. Single-crystal X-ray structures determined for three $C(OAr)_4$ derivatives confirm that the energies of the two conformers do not differ significantly. Thus, the two crystallographically nonequivalent molecules in the unit cell of tetraphenoxymethane (4) as well as of tetrakis(3,5-dimethyIphenoxy)methane (5) adopt conformations in which the central $C(OC)_4$ units have a near $D_{2d}$ symmetry, while the corresponding fragment has a distorted $S_4$ symmetry in tetrakis(4-bromophenoxy)methane (6). The experimental $C-O$ bond lengths and $C-0-C$ and $0-C-O$ angles are consistent with large anomeric interactions.

Item Type: Journal Article
Publication: Journal of American Chemical Society
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 12 Feb 2008
Last Modified: 19 Sep 2010 04:42
URI: http://eprints.iisc.ac.in/id/eprint/13011

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