Internal hydrogen bond, dynamics

In the next few sections, we describe the influence of a number of parameters aromatic resonance, lone-pair and dipolar repulsion, internal hydrogen bonding, electronegative substituents, and the surrounding solvent on the relative stability of tautomeric forms. The remainder of this chapter is devoted to a brief history of tautomeric equilibria and tautomer dynamics. 

Accurate predictions of solute interactions with a limited number of solvent molecules are possible using the supermolecular approximation. This is an approach based on the consideration of the dissolved molecule together with the limited number of solvent molecules as the unified system. The quantum-chemical calculations are performed on the complex of the solute molecule surrounded by as many solvent molecules as possible. The main advantage of the supermolecular approximation is the ability to take into account such specific effects of solvation as hydrogen bonding between the selected sites of the solvated molecules and the molecules of the solvent. In principle there are only two restrictions for the supermolecular approximation. One of them is the internal limitations of the quantum-chemical methods. The second restriction is the limitation of the current computer technology. Because of such restrictions this approximation coupled with ab initio molecular dynamics is possible only for small model systems.46-50... 

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