Group Electronegativities from Benzene Ring Deformations:  A Quantum Chemical Study

Abstract

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 S E and S R, are directly related to the electronegativity and resonance effects of the substituent, respectively. In the present paper, we show that S E 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 S E 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.

Topological Electronegativity Index and Its Application – I. Ionization Potentials of Alkyl Groups and Alkyl Halides

“…Matsunaga [7] also obtained the group electronegativity order of Me > Et > i-Pr > t-Bu (see Table 4) by analyzing experimental bond dissociation enthalpies. The group electronegativities obtained by Campanelli [20] and Matsunaga [7] are consistent with the experimental ionization potentials. From Table 4, it can be seen that the TEI is smaller than the group electronegativity values available in the literature [7,20], and the TEI order is in agreement with the order of group electronegativity in the literature [7,20].…”

“…Quite recently, Campanelli et al [20] proposed a new scale of group electronegativities, derived from benzene ring deformations in Ph À X molecules and by means of ab initio quantum chemical calculation, and got the group electronegativity order of Me > Et > t-Bu (see Table 4). Matsunaga [7] also obtained the group electronegativity order of Me > Et > i-Pr > t-Bu (see Table 4) by analyzing experimental bond dissociation enthalpies.…”

“…Quite recently, Suresh and Koga [19] reported a new method derived from the molecular electrostatic potential topography of substituted methanes for the calculation of atomic and group electronegativities. Campanelli et al [20] proposed a new scale of group electronegativities from the ring angles of 100 monosubstitued benzene derivatives, as determined by ab initio MO calculations at the HF/6 -31G* level. The semiempirical quantum chemical calculation needs a time-consuming parameterization, and the application of a high-level ab initio quantum chemical theory is very expensive [21].…”

Classical and reverse substituent effects in meta- and para-substituted nitrobenzene derivatives

“…Firstly, the nitro group is very electronegative (the group electronegativity in the Pauling scale, χ NO2 , is equal to 4.00 for a coplanar and 4.19 for a perpendicular orientation with respect to the benzene ring) [1] and as a consequence its strongly inductive effect influences the rest of the substituted molecule. Secondly, this group exhibits a great range of variability of its EA properties [2,3] with σ p = 0.78 and σ p − = 1.27 which dramatically depends on the kind of a moiety to which the group is attached [4].…”

Effect of Intra- and Intermolecular Interactions on the Properties of para-Substituted Nitrobenzene Derivatives

“…Its electron-accepting power (EAP) originates via two mechanisms. There is a strong inductive activity due to a combined effect of three electronegative atoms (the group electronegativity χ NO 2 is equal to 4.00 for coplanar and 4.19 for perpendicular orientation with respect to the benzene ring [5]). Furthermore, the two electronegative oxygen atoms cause an electron deficiency on the nitrogen atom and hence the nitro group may also act as a strong π-electron acceptor; the resonance power of the nitro group becomes significant when the electron-donating…”