Tautomerism in the Solid State

Abstract

Publisher Summary Proton tautomerism occurs readily in solution because there are no restrictions in fluid media on the conformational changes required for the tautomerization to take place. On the other hand, in the solid state, the mobility of molecular skeletons and protons is strictly limited. This is the main reason for tautomerizations being rarely observed in the solid state. One of the important factors for the feasibility of proton tautomerism in the solid state is the presence of an intra- or intermolecular hydrogen bond along which proton transfer takes place, accompanied by a switching of π-bonds. The presence of the hydrogen bond is not sufficient for observing proton tautomerism in the solid state. In fact, the tautomerization is likely to be frozen on the basis of the dipole–dipole interaction between tautomers. Proton tautomerism in the solid state is an ideal system to investigate cooperative phenomena concerning proton transfer, because tautomeric molecules are connected with each other in terms of dipolar and/or hydrogen-bonding interactions. Tautomerization plays a vital role in biological systems as well. The chapter describes the essence of proton tautomerism, focusing on the potential profile of proton transfer along the reaction coordinate of the tautomerization in the solid state.