Hydrogen-bonding interaction between acetic acid and pyridine 1:1 complex

Acetic acid (CH₃COOH) and pyridine (C₅H₅N) 1:1 complex was subjected to Density Functional Theory (DFT) calculations using 6-311G(d,p) basis set. Five equilibrium isomers were located, and the most stable structure has a strong NH–O hydrogen-bonding interaction. A normal-mode analysis of the vibrations of the five isomers was carried out and compared with the experimental values. The calculations indicate that solvents enhance significantly the strength of hydrogen bond as shown by the decrease of the N–H distance and appreciable red shift of the H–O vibration mode and blue shift of NH–O vibration mode.