CALCULATED ELECTROSTATIC POTENTIALS AND LOCAL SURFACE-IONIZATION ENERGIES OF PARA-SUBSTITUTED ANILINES AS MEASURES OF SUBSTITUENT EFFECTS

• Using an ab initio self-consistent-field molecular orbital approach, we computed 3-21G//STO-3G* and STO-5G//STO-3G* electrostatic potentials and average local ionization energies for 17 para-substituted anilines. Our results demonstrate that the most negative potentials (V(min)) and the local surface ionization energy minima (I(s,min)BAR) associated with the amine nitrogen lone pairs are highly sensitive indicators of the electron-donating and electron-attracting tendencies of the para substituents. We find excellent linear relationships between the 3-21G//STO-3G* amine nitrogen V(min) and I(S,min)BAR and the sigma(p)0 Hammett constants of the substituent X; the correlation coefficients are 0.99. Correlations of slightly lesser quality are shown to exist between V(min), I(S,min)BAR, and sigma(p)-, sigma(p), and pK(a). Estimates of previously unknown sigma(p)0 and pK(a) values are given. The presence of ring carbon I(S,min)BAR meta to the substituent X also provides a predictive capability for determining sigma(m) values.

Subject headings

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

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ref (subject category)

art (subject category)