Communication theory approach to the chemical bond

Recently proposed communication theory treatment of the chemical bond is outlined. The molecular systems in atomic resolution are interpreted as “communication” systems in which “signals” of the electron allocations to constituent atoms are propagated from the molecular input (source), e.g., the atomic promolecule reference, to the molecular output (receiver) via a network defined by the conditional two-electron probabilities. The electron delocalization accompanying the bond formation is responsible for the noise affecting the flow of information throughout the system. The conditional entropy and mutual information descriptors of such molecular communication channels are identified as overall measures of the covalent and ionic components of the system chemical bonds, and a distinction between the electron-sharing and coordination (donor–acceptor) bonds is investigated. These entropy/information descriptors of the chemical bond are illustrated in the two-electron, two-orbital model. This analysis covers the orbital and spin channels for the singlet (bonding) and triplet (nonbonding) states. The overall bond-order conservation in the model and the competition between the bond ionicity and covalency is stressed. The model polyatomic systems discussed include the π bonds in butadiene and benzene in the Huckel theory approximation. The predictions from the communication theory approach compare favorably with the chemical intuitive values and bond orders from other orbital approaches, e.g., the quadratic index of Wiberg and the two-electron multiplicities of the difference approach. The Hirshfeld partition of molecular electron density is briefly summarized and the average entropies of the local stockholder communication channel it generates are proposed as alternative information descriptors of the chemical bonds in molecules.