The hydration of aniline and benzoic acid: Analysis of radial and spatial distribution functions

摘要

Structural aspects of the hydration of aniline and benzoic acid in water were studied with 1D- and 3D-RISM integral equation methods. Analysis of the structural data reveals that the first hydration shell of aniline consists of ~26 water molecules, whereas benzoic acid is hydrated by 28.4 H_2O. For aqueous aniline the average number of water molecules surrounding the -NH_2 group is 6.7 and on average ~1.8 H-bonds are formed by the amino group. In aqueous benzoic acid the hydration shell of the -COOH group consists of 6.3 water molecules surrounding the carbonyl oxygen and of 6.1 water molecules around the hydroxyl group. The average number of H-bonds formed by the carboxylic group is 2.85. For both systems water molecules are preferably located above and below the plane defined by the phenyl ring at a distance of ~0.3 nm from the ring center. The number of the π-coordinated water molecules is 1.16 for aniline and 1.2 for benzoic acid. It was found, that the π-region of aniline is more H-bonded with water than the π-region of benzoic acid.