Abstract: The hydrogen bonds between the HCN and pyrrole were subjected to density functional theory (DFT) calculations using 6-311G(d, p) basis set. The structures and vibrational frequencies of the hydrogen-bonding complexes were computed at the B3LYP/6-311G(d, p) level. To obtain the accurate binding energies, single-point calculations were performed at the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ level, respectively. After BSSE (basic set superposition error) correction by the counterpoise method, the interaction energies of the complexes between HCN and pyrrole are －25.10, －19.30 kJ·mol－1 at MP2 level, respectively. The calculations indicate that solvents enhance significantly the strength of hydrogen bond as shown by the decrease of the N…H distance and cause appreciable red shift of the H－N vibration mode. The solvent effect is obvious when dielectric constant ε is within 1.5～30.0 and is weak when ε exceeds 30.0.

Key words: Density functional theory, BSSE, Dielectric constant