Electron density distributions of π bonds

A simple procedure for extracting the bent character and the π character of bonds from electron density maps is suggested. The ellipticity of π-double bonds, which is positive at the bond center, has opposite sign near the nuclei because of density accumulation in the σ plane. This is mainly due to σ-orbital contraction upon bond formation, and also due to the other atoms in the σ plane and to quantum mechanical σ and π interferences. The above mentioned density pattern is exhibited both by the total electron density and by the traditional difference density (with respect to spherically averaged independent atoms). The genuine chemical deformation density (i.e. with respect to independent atoms with optimally occupied p shell) shows density accumulation in the π direction everywhere along the bond path, also near the nuclei.