Topological properties of electron density in search of steric interactions in molecules : electronic structure calculations on ortho-substituted biphenyls

The bond critical points in the electron density are not necessarily associated with bonding interactions. When the distance between two atoms is smaller than their contact interatomic separation (CIS), an attractor interaction line passing through the corresponding bond critical point appears, indicating a nonbonding repulsive interaction. Sterically crowded molecules are defined as those possessing such interaction lines at their equilibrium geometries