Intermolecular orbital repulsion effect on the blue-shifted hydrogen bond

This work suggests a possible phenomenon of the blue-shifted hydrogen bond, which is due to the compression caused by two opposite type of interactions in X–H⋯Y system (Benzene⋯H–F and T-shaped benzene dimer have been considered as model systems). One type is the attraction between H-bond acceptor and remote part of H-bond donor and the other type is the repulsion between X–H and H-bond acceptor. The results obtained from molecular orbital interactions reveal that the repulsive four-electron-two-orbital interactions between the σX–H orbitals of H-bond donor and the occupied orbitals of H-bond acceptor play an important role towards characterization of blue-shifted hydrogen bond with shortening of the X–H bond.