The intramolecular proton transfer (PT), the water-assisted PT, and the methanol-assisted PT of 2-[(4-chlorophenylimino)methyl]-8-hydroxyquinoline are investigated. Based on the crystal structure of the Schiff base compounds, the intramolecular PT, the water-assisted PT, and the methanol-assisted PT of 2-[(4-chlorophenylimino)methyl]-8-hydroxyquinoline are investigated at B3LYP/6-31＋G(d) basis set level. The primary geometry structures, infrared frequencies, energies as well as the NMR data are compared. It implies that both the water and methanol are involved in the proton transfer processes through hydrogen bonds, and seven-membered cyclic transition states are formed, which are favorable for PT owing to their capability to reduce significantly the PT energy barriers. The H-bonds play a key role in decreasing the activation energy.

Key words: 2-[(4-chlorophenylimino)methyl]-8-hydroxyquinoline, proton transfer, transition state, hydrogen bond, activation energy