IRREGULAR ORDER IN BASICITIES OF METHYLAMINES IN AQUEOUS-SOLUTION - ARISM-SCF STUDY

The irregular order in basicities of a series of methylamines in aqueo us solution is studied by means of an ab initio quantum chemical calcu lation combined with the extended reference interaction site method in statistical mechanics of molecular liquids (RISM-SCF method). By usin g the restricted Hartree-Fock level approximation in the theoretical t reatment for solute electronic structure, the irregular order in basic ities is reproduced in qualitative agreement with well-established exp erimental results. The method does not require a priori cavity assumpt ion in solution, which introduces ambiguous parameters into the theori es and enables us to explain the physical origin of the basicity entir ely from a microscopic point of view. Solvation structures around meth ylamines are also examined in terms of radial distribution functions. The result is an encouraging indication of the potential usefulness of the RISM-SCF approach to investigate a variety of quantum processes i n solution.