Orbital interactions through space and through σ-bonds

The present state of one of the comparatively new theoretical concepts in organic chemistry – the interaction of two heteroatoms having a lone electron pair or of groups incorporating a π-bond through the system of σ-bonds separating them – is considered. Two mechanisms of such interactions are discussed – through space and through the σ-bonds. These interactions are assessed in terms of UV, photoelectron, and electronic transmission spectroscopic and quantum-chemical data. The influence of the above interactions on the reactivity of the molecules is illustrated. The bibliography includes 139 references.