Concerning the Electron-Withdrawing Power and the Electronegativity of Groups

Abstract

The polar substituent constants, σ^*, obtained recently by Taft from reactivity considerations are discussed. Several qualitative relationships of σ^* values to substituent constitution are established. These relationships relate quantitative correlations of the effect of structure on reactivity to concepts of bonding and electronegativity. The Mulliken concept of electronegativity is supported. The relatively large electron‐withdrawing powers of Cl, Br, and I in bonds to carbon suggest the participation of the d orbitals of the valence shell. A discrepancy is noted between σ^* values (and Mulliken's electronegativities) and the group electronegativities proposed by Dailey and Shoolery on the basis of proton nuclear magnetic resonance shifts in ethyl and methyl derivatives.