Chemical Notions from the Electron Density.

The study of density and the role played by its atomic representation is proposed as a way for the rationalization of chemical behavior. As this behavior has been long rationalized in terms of the basic concepts of empirical structural chemistry, a direct link between both approaches is searched for by using the exact representation of the density provided by the deformed atoms in molecules method (Rico, J. F.; López, R.; Ema, I.; Ramírez, G.; Ludeña, E. J. Comput. Chem. 2004, 25, 1355-1363). Noting that the spherical terms of the pseudoatoms cannot be mainly responsible for the chemical behavior, we study the small nonspherical deformations and find that they reflect and support all basic concepts of empirical structural chemistry. Lone pairs; single, double, and triple bonds; different classes of atoms; functional groups; and so forth are paralleled by the density deformations in a neat manner. These facts are illustrated with several examples.