Intramolecular Twisting Effects in Substituted Benzenes. II. Ground-State Properties

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Abstract
The effects on ground-state properties of twisting a substituent group about the substituent-ring bond in substituted benzenes are discussed from the viewpoint of semiempirical MO theory. The ground-state properties are discussed with reference to a parameter θ, which generally increases as the substituent is twisted. The substituent-ring bond order varies approximately as cosθ, and the following vary approximately as cos2θ: the resonance energy, charge densities, ring C–C bond orders and the π-electronic dipole moment. The θ dependence of the total dipole moment is discussed. Numerical applications to N,N-dimethylaniline and related molecules are described, including a detailed treatment of the dipole moments of N,N-dimethylaniline and some of its ortho-substituted derivatives. A brief discussion of the valence state of the dimethylamino group is included.