摘要：

Substituent effect of reactive intermediates has long been a central issue in organic chemistry^[1]. While quantitative knowledge on structure-property relationship of close-shell species (e.g., carbanions, carbocations, and neutral molecules, etc.) has already been well documented in the literature and textbooks, the present understanding of substituent effect on radicals is still largely limited to the information drawn basically from the (σ and BDE (bond dissociation energy) studies of a single family, the benzyl radical^[2]. Naturally, the general applicability of these scales as indicators of radical stability to other families bearing different structural features needs to be examined. The present systematic experimental and computational investigation on radicals of the benzylic type centered on carbon atoms of vaiying degree of electronegativity shows that i) there are actually three (rather than one as previously well claimed) basic patterns of radical substituent effect for carbon radical; and ii) prediction of the direction and magnitude of radical substituent effect should be workable on the basis of quantitative understanding of polar interactions within a radical system^[3]. Experimental evidence and detailed analysis on this respect are presented.

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