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Ab initio quantum chemistry methods were applied to study the bifurcated bent hydrogen bonds Y… H2CZ (Z = O, S, Se) and Y…H2CZ2 (Z = F, Cl, Br) (Y = Cl-, Br-) at the MP2/6-311++G(d,p) and MP2/6-311++G(2df,2p) levels. The results show that in each complex there are two equivalent blue-shifted H-bonds Y…H—C, and that the interaction energies and blue shifts are large, the energy of each Y…H—C H-bond is 15-27 kJ/mol, and Δr(CH) = -0.1 - -0.5 pm and Δv(CH) = 30 - 80 cm-1. The natural bond orbital analysis shows that these blue-shifted H-bonds are caused by three factors: large rehybridization; small direct intermolecular hyperconjugation and larger indirect intermolecular hy- perconjugation; large decrease of intramolecular hyperconjugation. The topological analysis of elec- tron density shows that in each complex there are three intermolecular critical points: there is one bond critical point between the acceptor atom Y and each hydrogen, and there is a ring critical point inside the tetragon YHCH, so these interactions are exactly H-bonding.
Ab initio quantum chemistry methods were applied to study the bifurcated bent hydrogen bonds Y ... H2CZ (Z = O, S, Se) and Y ... H2CZ2 (Z = F, Cl, Br) MP2 / 6-311 ++ G (d, p) and MP2 / 6-311 ++ G (2df, 2p) levels. The results show that in each complex there are two equivalent blue- shifted H-bonds Y ... H- C, and that the interaction energies and blue shifts are large, the energy of each Y ... H-C H-bond is 15-27 kJ / mol and Δr (CH) = -0.1 -0.5 pm and Δv (CH) = 30 - 80 cm-1. The natural bond orbital analysis shows that these blue-shifted H-bonds are caused by three factors: large rehybridization; small direct intermolecular hyperconjugation and larger indirect intermolecular hy- perconjugation; large decrease of intramolecular hyperconjugation. The topological analysis of elec- tron density shows that in each complex there are three intermolecular critical points: there is one bond critical point between the acceptor atom Y and each hydrogen, and there is a ring critical point i nside the tetragon YHCH, so these interactions are exactly H-bonding.