The prominent enhancing effect and mechanism of the methyl group in the X···Y (X=O, S, H₃CO, H₃CS, (H₃C)₂O, (H₃C)₂S; Y=HCN, HNC) hydrogen-bonded complex

Abstract

An ab initio computational study of the enhancing role of the methyl group in the M···H (M=S and O) hydrogen bond has been carried out at the QCISD/6-311++G(2df,2p) level. The bond lengths, frequency shifts, and interaction energies were analysed. The methyl group of the electron donor plays a positive role in the formation of the hydrogen bond. Its enhancing role is stronger in the O···H hydrogen bond than in the S···H hydrogen bond. The results show that the methyl group has a prominent effect on the strength of the hydrogen bond. The interaction energy is increased by 347% for the Me₂O–HCN complex relative to that for the O–HCN complex. The enhancing mechanism of the methyl group has been analysed by means of natural bond orbital (NBO) theory. The electrostatic interaction is of more importance to the O···H hydrogen bond, whereas dispersion and charge-transfer interactions play a more significant role in the S···H hydrogen bond.

Keywords:

• methyl group
• hydrogen bond
• enhancing effect
• mechanism
• NBO

Acknowledgements

This work was supported by the National Natural Science Foundation of China (20973149) and the Scientific and Technological Innovation Fund for College Students (090509), Yantai University, China. It was also supported by the Outstanding Youth Natural Science Foundation of Shandong Province (JQ201006).