Electrostatic effects on disproportionation equilibria: dihalogeno and methyl derivatives of benzene

The disproportionation equilibria of benzene derivatives X—Ph—Y (X, Y = F, Cl, CH3) in the gas phase, were calculated from their enthalpies and entropies of formation at 298 K. Calculations of the electrostatic energy based on the point charges approximation method predict reasonably well the reaction enthalpies of all meta-benzene derivatives and predict nearly as well the other fluoro- and methyl-derivatives. The theory fails if strong resonance and/or steric interactions are present. The generally better ability of the electrostatic theory to treat disproportionation or conformational equilibria than the proton transfer reactions is also discussed.