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Steric effects on the ultraviolet absorption of 1,2-enedioic and related systems

Balasubrahmanyam, Natarajan S and Rao, Surya Prakash H (1978) Steric effects on the ultraviolet absorption of 1,2-enedioic and related systems. In: Proceedings of the Indian Academy of Sciences - Section B, 87 (5). pp. 371-388.

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Abstract

1,2-Enedioic systems, being sterically perturbed from planarity do not show the effect of the extended conjugation expected of a (formal) trienic entity. In the absence of a model which approximates to a uniplanar situation, the strategy of replacing an ester group in the enedioates by a cyano (for which less stringent steric demand may be presumed) and noting the correction concomitant to this replacement was adopted to arrive at a notional figure for the position of maximal absorption in the planar enedioates. From this the conclusion, subject to substantiation by molecular mechanical or quantum chemical calculations, was drawn that even the E-isomeric and comparatively less substituted enedioates are highly sterically perturbed. An alternative to an earlier explanation of the bathochromic shift of absorption maxima encountered in the 5-cyclic ene-ester and ene-nitrile, relative to the 6-cyclic analogues (observed also with the enedioates and cyanovinyl ester systems), seen later to have been based on unwarranted premises, has been advanced. A comment on the absorption characteristics of enedioic anhydrides has been appended.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Springer.
Keywords: Enedioates - cyanovinyl esters - ene-anhydrides - ultraviolet spectra - steric effects - rotomerisation of ester groups - time-dependent solvent effect
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Date Deposited: 23 Aug 2010 06:03
Last Modified: 19 Sep 2010 06:14
URI: http://eprints.iisc.ernet.in/id/eprint/31459

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