Effect of substituents on the chemical shift of benzylic protons: evidence for a conformational dependence

The benzyl proton shifts in 11 series of para-substituted toluenes bearing different α substituents have been determined. In each series, a plot of the benzylic shift against the Hammett σ values of the para-substituent is linear. The slope of these plots varies from 0.2 to 0.0 p.p.m./σ. The variati...

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Bibliographic Details
Published inCanadian journal of chemistry Vol. 46; no. 9; pp. 1595 - 1598
Main Authors Fraser, Robert R, Gurudata, Reyes-Zamora, Cesar, Swingle, Robert B
Format Journal Article
LanguageEnglish
Published Ottawa, Canada NRC Research Press 01.05.1968
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Summary:The benzyl proton shifts in 11 series of para-substituted toluenes bearing different α substituents have been determined. In each series, a plot of the benzylic shift against the Hammett σ values of the para-substituent is linear. The slope of these plots varies from 0.2 to 0.0 p.p.m./σ. The variation is found to be conformationally dependent, a fact which is not explicable by current theory. A hyperconjugative interaction is proposed to account for these results and for several anomalies in the literature.
ISSN:0008-4042
1480-3291
DOI:10.1139/v68-266