EVALUATION OF GROUP ELECTRONEGATIVITY BY PAULING THERMOCHEMICAL METHOD

Pauling's bond energy equation, D(H-G) = [D(H-H) D(G-G)]1/2 + K(Δχ)2 (1), is applied to some 28 HG molecules, where H is hydrogen and G any group of atoms, to calculate the electronegativity (χG) of a group. In eq 1 D(H-G), D(H-H), and D(G-G) are the energies of the H-G, H-H, and G-G bonds, respectively, Δχ = |χH - χG|, and K is a constant. The value of K is optimized to 25 in order to obtain maximum amount of correlation (r = 0.960) of the χG values for some 19 groups/atoms with the 1JCC(ortho-ipso) coupling constants in monosubstituted benzenes. These 1JCC constants form a very good experimental scale for group electronegativity. With Inamoto's "i" scale, derived experimentally, the χG values for some 20 groups/atoms correlate quite satisfactorily (r = 0.936). However, Δχ for two groups, CH(OH)CH3 and Si(CH3)3, out of the 28 groups considered are found to be imaginary, for which the bond energy data are held partially responsible. The effects of various bond-determining factors on the χG values evaluated by eq 1 are examined critically. It is concluded that, when the order of the G-G bond is 1 as in H-H or H-G, the method yields a reasonable value for the electronegativity of a group. © 1990 American Chemical Society.