Charge demands of electron-withdrawing groups: evidence for a saturation effect

Abstract

Estimates of charge demands q_x(the fraction of π charge withdrawn by the electronegative functionalities X in X₂CH^–) are obtained through a charge–δ(¹³C) relationship and are shown to be additive for predicting the ¹³C shift of the carbanionic carbon atom in XYCH^–: the facts that such values are less than those for PhCH–X and that the combined effect of the two phenyl groups in Ph₂C–X is almost the same as that of one phenyl in PhCH–X in delocalizing the charge are attributed to saturation phenomena.