Hydrogen bonding. Part 86: DFT molecular orbital study of the first hydration shell of N, N, N-trimethyl-1-adamantylammonium ion

Abstract

Consecutive addition of H 2O to the N, N, N-trimethyl-1-adamantylammonium ion (3MAA +) follows an orderly pattern. The first H 2O binds to the triangular face formed by the three methyl groups. Subsequently three sets of three H 2O bind sequentially to form, in order, (H 2O) 3, (H 2O) 6, and (H 2O) 9 subgroups with C 3 symmetry about the z-axis of the ion. The result is a closed C 3 (H 2O) 9 ring about the ion in the region adjacent to the α-CH 3 and β-CH 2 carbons, to give a first shell stoichiometry of 3MAA +·10H 2O. These 10H 2O are bound to the ion by a combination of CHO hydrogen bonds and ion–dipole forces. The eleventh H 2O accepts a hydrogen bond from a ring H 2O but is otherwise unconnected to the ion, and is assumed to represent the first member of a larger solvent shell.