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# \sigma-Correlations and steric effects

Balasubrahmanyam, SN and Mallick, IM (1982) \sigma-Correlations and steric effects. In: Organic Magnetic Resonance, 19 (3). pp. 160-163.

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## Abstract

Carbon-1 shifts in 1-dimethylimino-3-dimethylamino-1-(4-substituted)phenylprop-2-ene perchlorates show high correlation and negative dependence v. a \sigma set having high f character, similar to \alpha and carbonyl carbon shifts in 4-substituted styrenes and N,N-dimethylbezamides, respectively. In sharp contrast with the \beta -carbons of the styrenes and the 15N absorptions of benzamides, whose shifts show high positive correlations with specific ratios of f and R characters, the C-2 shifts remain invariant. In the correlation of the barriers about the N-CO bond in N,N-dimethylbenzamides v. f R, the R effect has been reported to increase dramatically for the meta-series when values determined in acetonitrile are exchanged with those determined in chloroform and, in the para series, to be higher than (normal) in both solvents. \alpha -Carbon shifts in tris-para-substituted triphenylcarbonium ions correlate with an \sigma set having exceptionally high R character (c. 98 %). Explanations, based mainly on the likely action of steric factors, are suggested.

Item Type: Journal Article The copyright of this article belongs to Heyden & Son Ltd. Division of Chemical Sciences > Organic Chemistry 25 Oct 2005 27 Aug 2008 11:31 http://eprints.iisc.ernet.in/id/eprint/3869

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