A theoretical study of N–H ··· π H-bond interaction of pyrrole: from clusters to the liquid

Abstract

The N–H ··· π H-bond interactions of clusters and liquid formed by pyrrole molecules were investigated by Quantum Mechanics (QM) and classical Molecular Dynamics (MD), respectively. Based on the optimized geometry at the B97-D/aug-cc-pVTZ level of theory including dispersion correction, the nature and the origin of N–H ··· π H-bond interactions were unveiled by atoms in molecules (AIM), natural bond orbital (NBO), and energy decomposition analysis (EDA). Among them, the AIM analysis gives evidence to the presence of N–H ··· π H-bond interactions, the NBO examination reveals that π → σ* donor-acceptor orbital interaction is of great importance. EDA study indicates that N–H ··· π interactions are governed by the electrostatic and dispersion term. Meanwhile, MD simulation with OPLS-AA (optimized potentials for liquid simulations all-atom) was applied to study the pure liquid pyrrole at different temperature. The results confirm the existence of the N–H ··· π H-bond in the pure liquid pyrrole, and further characterized the structures of this H-bond which is somewhat different to the clusters.

Keywords:

• N–H ··· π H-bond
• pyrrole cluster
• liquid pyrrole
• QM and MD

Acknowledgements

The authors thank Dr Tian Lu at the Institute of Chemical and Biological Technology, University of Science and Technology Beijing for helpful discussions. The computational support of the Gaussian from the School of Chemical and Environmental Sciences, Henan Normal University and Professor Xiaopeng Xuan are much appreciated.