Effects of solvation on the pairing of electrons in a series of simple molecules and in the Menshutkin reaction

The effects of solvation on the pairing of electrons in molecules have been analyzed in a series of molecules and in the Menshutkin reaction between a mmonia and methyl chloride. Solvation in water and chloroform has been mode led by means of the polarizable continuum model. A comparative analysis of the electron-pair structure of all the molecules studied has been carried o ut in the framework of the atoms in molecules theory. In particular, atomic populations and localization and delocalization indices have been used for describing the electron-pair characteristics of all the molecules. In gene ral, this analysis shows that solute-solvent interactions modify the electr on-pair distribution of the solute increasing the polarization of the molec ular bonds. The electron-pair characteristics of the different stationary p oints found in the Menshutkin reaction have been also analyzed in detail. T he evolution of electron pairing along the reaction path has also been foll owed in vacuo and in water, Comparison of the results obtained reveal that the main difference between the reaction in gas phase and in water is the s tructural and electronic advance of the transition state towards the reacta nt side. Finally, the Menshutkin reaction with explicit representation of t he solvent molecules has been studied to discuss the relevance of charge-tr ansfer and specific interactions between the solvent and the solute.