Janssen Pharmaceutica, Research Laboratories, BeerseBelgium
Abstract:
The X(X) values1 of the halogens (which resemble the Pauling electronegativities) and of some oxa substituents can be interpreted in terms of the inductive and resonance parameters σI and σoR according to the regression equation and η*R=η(X)?η(R) it is found that for some substituted methyl, phenyl and benzoyl groups σ*]XR=αηXR where α equals ?10.6 and ?10.9 for R = Me and R = Ph, CHO and PhCO respectively. Thus σ*]XRand ηxr represent Taft σ* and σI(X)?σoR(X)] values relative to that of the parent R group. The hydroxyl frequencies of phenol, and benzoic, acrylic, acetic and formic acids measured in dilute carbon tetrachloride solutions correlate with σI(X) and σoR(X) according to the equations v(OH) = ?423.0 σI(X) + 3654.7 v(OH) = ?270.0 σ0R(X) + 3586.7 where X = Ph, PhCO, CH2=CHCO, MeCO and HCO. From these results, it is inferred that the σ* values of substituents having an α sp2 hybridized carbon atom are proportional to σ0R according to the equation σ*(X) = 3.97 σ0R(X) + 1 New σI σoR and σ* values of some acyi, benzoyl and substituted phenyl groups are presented.