Abstract
Spectroscopic evidence is used to show that phenyl radicals are only weakly conjugated with central atoms (S, P, As, Sb, Si, Sn, Pb) not having unshared valence electrons. No resonance interaction is encountered between several phenyl radicals attached to such a central atom, and each phenyl radical makes an independent contribution to the molar extinction coefficients. If the central atom (S, N, P, As, Sb, Bi) has an unshared pair of electrons, extensive conjugation between the phenyl radicals occurs and leads to spectra in sharp contrast to those of simple benzene derivatives. No simple relation exists between the spectra of closely related compounds with different numbers of phenyl radicals attached to the same central atom. The near ultraviolet absorption spectra of dimethylaniline, methyldiphenylamine, triphenylamine, triphenylarsine, triphenylstibine, triphenylbismuthine, triphenylarsine oxide, and triphenylstibine dichloride are reported and compared with those of related compounds of phosphorus, sulfur, and group IVA elements.