On the definition of valence of functional groups in molecules

Abstract

The quantum chemical definition of valence as a property of an atom in a molecule was generalized to functional groups in molecules. The new definition was applied to a series of functional groups in simple organic molecules. The results were found to be in agreement with expectation on the basis of classical valence rules. CH₂, N₂ and CO group valences in selected organic molecules are compared. Group valences for systems violating the classical valence rules are also briefly discussed with an emphasis on the role of multicenter bonding in the phenomenon of hyper- and subvalence. Finally, Si₂ groups serve to probe the bulk character of small and medium silicon clusters.