Substituted anilines: The tug-of-war between pyramidalization and resonance inside and outside of crystal cavities

Efficient rehybridization at nitrogen provides a convenient conceptual framework for rationalizing structural and electronic effects in substituted anilines. Computations predict that a subtle balance between hybridization and conjugation in substituted anilines is easily perturbed by remote substitution. Rehybridization correlates with electronegativity of substituents as predicted by the Bent's rule even though the substitution is not direct but mediated by an aromatic system. Use of the sigma(-) Hammett parameters significantly improves the description of substituent effects. Limitations of X-ray crystallography in studies of subtle electronic structure effects are shown through comparison of computational geometries with crystallographic data which illustrates how supramolecular forces associated with the crystal packing mask intrinsic electronic preferences. (c) 2007 Elsevier B.V. All rights reserved.