Electronic properties of multifurcated bent hydrogen bonds CH3...Y and CH2...Y.
H-bonding angle angleYHX has an important effect on the electronic properties of the H-bond Y...HX, such as intra- and intermolecular hyperconjugations and rehybridization, and topological properties of electron density. We studied the multifurcated bent H-bonds of the proton donors H3CZ (Z = F, Cl, Br), H2CO and H2CF2 with the proton acceptors Cl(-) and Br(-) at the four high levels of theory: MP2/6-311++G(d,p), MP2/6-311++G(2df,2p), MP2/6-311++G(3df,3pd) and QCISD/6-311++G(d,p), and found that they are all blue-shifted. These complexes have large interaction energies, 7-12 kcal mol(-1), and large blue shifts, delta r(HC) = -0.0025 --0.006 A and delta v(HC) = 30-90 cm(-1). The natural bond orbital analysis shows that the blue shifts of these H-bonds Y...HnCZ are mainly caused by three factors: rehybridization; indirect intermolecular hyperconjugation n(Y) -->sigma*(CZ), in that the electron density from n(Y) of the proton acceptor is transferred not to sigma*(CH), but to sigma*(CZ) of the donor; intramolecular hyperconjugation n(Z) -->sigma*(CH), in that the electron density in sigma*(CH) comes back to n(Z) of the donor such that the occupancy in sigma*(CH) decreases. The topological properties of the electron density of the bifurcated H-bonds Y...H2CZ are similar to those of the usual linear H-bonds, there is a bond critical point between Y and each hydrogen, and a ring critical point inside the tetragon YHCH. However, the topological properties of electron density of the trifurcated H-bonds Y...H3CZ are essentially different from those of linear H-bonds, in that the intermolecular bond critical point, which represents a closed-shell interaction, is not between Y and hydrogen, but between Y and carbon.
Li
An Yong
AY
School of Chemistry and Chemical Engineering, Southwest University, 400715, Chongqing, P. R. China. aylifnsy@swu.edu.cn
Yan
Xiu Hua
XH
D001966:Bromine / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D004583:Electrons; D005461:Fluorine / Q000737:chemistry; D005557:Formaldehyde / Q000737:chemistry*; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry; D006860:Hydrogen Bonding; D008697:Methane / Q000031:analogs & derivatives / Q000737:chemistry*; D008956:Models, Chemical; D011789:Quantum Theory
D006845:Hydrocarbons, Fluorinated; D005557:Formaldehyde; D005461:Fluorine; D002713:Chlorine; C102075:difluoromethane; D008697:Methane; D001966:Bromine