The valence bond description of conjugated molecules i.SCFlevel

Aiming at developing an approximate method to get good quality valence bond functions for any closed‐shell delocalized system, we analyze their SCF functions in terms of weighted bonding schemes, and investigate the general rules relating the weights of ionic structures to those of covalent ones. The butadiene case is treated in details, and the results are generalized to all closed shell singlet conjugated molecules. It is demonstrated that, contrary to what an intuitive generalization of the two‐electron‐two‐center model would predict, each bond is not described as a half‐covalent, half‐ionic entity, but that the ionic component is significantly preponderant. Some consequences on the behavior of conjugated systems under the influence of an electric field are discussed.