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

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 similar to 26 water molecules, whereas benzoic acid is hydrated by 28.4 H2O. For aqueous aniline the average number of water molecules surrounding the -NH2 group is 6.7 and on average similar to 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 similar to 0.3 nm from the ring center. The number of the pi-coordinated water molecules is 1.16 for aniline and 1.2 for benzoic acid. It was found, that the pi-region of aniline is more H-bonded with water than the pi-region of benzoic acid. (C) 2012 Elsevier B.V. All rights reserved.