Theoretical study of different substituent benzenes and benzene dimers blue-shifted hydrogen bonds

Density functional theory (DFT) optimizations at M06-2X/6-31++G (d, p) level had been performed in the T-shaped structures of C6H5R (R = NO2, F, H, OH, CH3, and NH2) with benzene complexes. The interaction energies were calculated by counterpoise (CP)-corrected methods. Among the six dimers, we can see that the C–H⋯π bonded of C6H5NO2⋯benzene complex is the most stable one. Furthermore, the C–H⋯π blue-shifted hydrogen bonds in the dimers were studied. All the C–H bonds of the proton donors showed behavior of the contraction. And the different substituent groups had some effect on the contraction of the C–H bond. In addition, the natural bond orbital (NBO) and atoms in molecules (AIMs) analysis were investigated the origin of C–H⋯π blue-shifted hydrogen bond. From the NBO analysis, it was found that a negligible increase of electron density (ED) on the σ* (C–H) orbital and an increase of an s character of the C–H bond upon complexation were responsible for contraction and strengthening of this C–H bond. The AIM analysis showed that all studied dimers in this paper satisfied the indicative criteria of hydrogen bonding interactions and it was necessary to supplement those criteria with information on the changes in the electron density of the donor X–H bond occurring upon complexation to differentiate between H bonding and anti-H bonding.