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Anisochrony of O-methylene protons of ethyl ester functions and structural factors in the connected chiral entities

Balasubrahmanyam, SN (1986) Anisochrony of O-methylene protons of ethyl ester functions and structural factors in the connected chiral entities. In: Journal of Chemical Sciences, 96 (1-2). pp. 21-58.

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(i) Incistrans pairs of cyclic 1,3-dicarboxylic acid ethyl esters thecis-foms exhibit higher O-methylene proton (HA, HB) anisochrony than thetrans-forms; (ii) anisochrony, easily observed in certain decalin-10-carboxylic ethyl esters, ‘disappears’ on one of the rings attaining the possibility of transforming into a ‘twist’ form; (iii) in certain pairs of chiralsecethyl esters and theirtert-methylated analogues anisochrony is higher in the latter, contrary to expectation, while, in certain others, the reverse is observed. Attempted explanations are based on assessments whether H A and H B are or are not in highly different magnetic environments in confomers regarded as preferred. This subsumes the possibility thatXYZC-CO2H A H B Me chiral ethyl acetates differ fromXYZC-CH A H B Me ethanes because intervention by the carboxyl group insulates the prochiral centre and allows anisotropic effects to gain somewhat in importance among mechanisms that discriminate between H A and H B so long as rotamerpopulation inequalities persist. Background information on why rotamer-population inequalities will always persist and on a heuristic that attempts to generalize the effects ofXYZ inXYZC - CU AUB V is provided. Possible effects when connectivity exists between a pair amongX, Y, Z or when specific interactions occur betweenV andX, Y orZ are considered. An interpretation in terms of ‘increasing conformational mobility’ has been suggested for the observed increase in the rate of temperature-dependence of O-methylene anisochrony down a series of chiral ethyl esters.

Item Type: Journal Article
Publication: Journal of Chemical Sciences
Publisher: Indian Academy of Sciences
Additional Information: Copyright of this article belongs to Indian Academy of Sciences.
Keywords: Anisochrony of geminal sensors;‘intrinsic’ asymmetry (diastereotopism);gradient of anisotropy;Binsch heuristic;conformational analysis;internal conformation of ester groups;rotamerization of secondary and tertiary ester functions;H-bonding effects.
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Date Deposited: 03 Sep 2009 09:24
Last Modified: 03 Sep 2009 09:24
URI: http://eprints.iisc.ac.in/id/eprint/22778

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