Non-conventional hydrogen bonds: A brief review of blue shift or red shift of C-H stretching frequency

The results show that the O atom, as compared to the S, Se, and Te ones acting as proton acceptors, plays a peculiar role in the C-H blue shift of stretching frequencies involving hydrogen bonds. It is found that the magnitude of red- or blue-shift of the C-H stretching frequency in the hydrogen bond is mainly determined by the C-H polarity (DPE) and gas phase basicity (PA) of the proton acceptor in the isolated isomer, besides relevant weak interactions and the geometrical structure of the formed complex.