Partial communication channels of molecular fragments and their entropy/information indices

Within the ' communication' theory of the chemical bond the additive decomposition of the global entropy/ information indices into corresponding quantities characterizing the partial communication channels of the embedded molecular fragments is examined. The so called row and column channels of molecular subsystems are introduced. They represent alternative communication networks of the constituent fragments in the molecule, which fully take into account the internal ( intra- subsystem) and external ( between the molecular fragment and its molecular environment) communications ( bonds). These concepts are illustrated using the two- orbital model of a chemical bond. The three- orbital model of the triatomic, symmetric transition- state complex is then examined to explore the influence of the system spin polarization on the entropy/ information bond descriptors of the internal and external chemical interactions of the model diatomic fragments. Applications to the pi- bond systems ( butadiene and benzene) in the Huckel theory approximation are also reported and the results are compared with predictions from molecular orbital ( MO) theory. These results indicate that the information- theoretic indices of the partial channels of molecular fragments emphasize the information equilibrium of the molecular subsystems, which is manifested by a remarkable equalization of various atomic and diatomic indices, irrespective of the fragment identity. This is in contrast to the complementary MO bond indices, which strongly differentiate between different subsystems, in accordance with the molecule structural formula.