Quantum Mechanical Calculations of Electrical Effects of Substituents in para-Substituted Anilines

Abstract

Base strength measurements with substituted anilines indicate direct conjugation between the amino groups and electron-attracting unsaturated substituent groups such as —NO_2,—C≡N, etc. (I). Such conjugation delocalizes the unshared electron pair of nitrogen and confers a formal (+) charge on the amino group. Somewhat analogous behavior might be anticipated for substituents which do not carry multiple bonds but which, like tercovalent boron, could accept an electron pair (II) or, like a positively charged trimethylammonium group, could stabilize an adjacent negatively charged center as in the “ylides” (III). Resonance forms may be written which symbolize each of these situations (I-III).