Topological and NBO analysis of hydrogen bonding interactions involving C–H⋯O bonds

Abstract

Ab initio calculations are used to analyze the effect of C–H⋯O hydrogen bonding interactions on the C–H bond length. Methane derivatives, CH4−nXn (where n=1,2,3 for X=F and n=1 for X=NO2) are taken as proton donors and H2O as acceptor. The topological properties of electronic charge density are analyzed employing the Bader's Atoms In Molecules (AIM) theory. A good correlation between the structural parameters and the properties of charge density is found. Then, using the Natural Bond Orbitals (NBO) approach, the effects of charge transfer interactions on the behavior of the C–H bond are investigated. It is found that the competitive effects between intermolecular nO→σ(C–H)∗ and intramolecular nF→σ(C–H)∗ of charge transfer interactions in the CH4−nFn/H2O systems causes a decrease of the σ(C–H)∗ antibond occupation number, and concomitantly, a contraction of the corresponding C–H bond. In the NO2CH3/H2O system, the only charge transfer interaction, the nO→σ(C–H)∗ intermolecular interaction cause a increase of the σ(C–H)∗ antibond occupation number which entails a slight lengthening of the corresponding C–H bond.