Theoretical Study of Methylation Substitution Effect on Hydrogen Bonding Strength in the Carboxylic Acid, Amine and Water Three Molecular System

摘要

This research uses the Gaussian 03 program and adopts the density functional theory (DFT) B3LYP/6-311+G(2d,p) calculation method to explore methylation effect on the strength of hydrogen bonding among the carboxylic acid-amine-solvent medium weakly bound molecular system. It was found that the more methyl groups substitute the amine hydrogen, with existence of the water medium, the stronger for the H-bonding constructed between carboxyl and amino functional groups and the corresponding strength was stepwise increasing. The characteristic enhancement for hydrogen bonding strength leads the acidic hydrogen to dissociate easily from the carboxylic acid. The self-developed INDO program was applied for use herein. The "Localized H-bond population analysis" computed bond energy and bond order of localized H-bond, auxiliary discuss the changes of the H-bonding among research system.