Group Electronegativities from Benzene Ring Deformations: A Quantum Chemical Study

We propose a new scale of group electronegativities, derived from benzene ring deformations in Ph-X molecules. A recent analysis of such deformations (Campanelli, A. R.; Domenicano, A.; Ramondo, F. J. Phys. Chem. A 2003, 107, 6429) has shown that two orthogonal linear combinations of the internal ring angles, termed SE and SR, are directly related to the electronegativity and resonance effects of the substituent, respectively. In the present paper, we show that SE increases linearly with the electronegativity of X within each of the first two rows of the periodic table, acting as a sensitive indicator of the polarity of the Ph-X bond. By using SE values from ab initio quantum chemical calculations, we have derived the electronegativities of 100 organic and inorganic groups. Nonbonded interactions with the ortho hydrogens and carbons may fictitiously alter the electronegativity of a group; in most cases, however, they are easily eluded by changing the conformation of the substituent with respect to the benzene ring. Although the atom directly linked to the ring tends to dominate the electronegativity of a group, the role of its adjacent atoms is also important. Their effect depends markedly on the nature of chemical bonding and electron density distribution within the group.