General Principles of the Design of Tautomeric Systems

Abstract

Analysis of the concept of tautomerism, of the domain of chemical transformations regarded as tautomeric and the detailed examination of the carbonotropic tautomerism reactions makes it possible to attempt the formulation of general principles of target-oriented construction of tautomeric systems on the basis of migration processes.In its essence, this task consists in the prediction and design of a reversibl)!equilibrated molecular system whose thermodynamic and activation parameters correspond to the commonly accepted scale of tautomeric processes (Equation (1.5». A simplified, though costly, approach is, in principle, possible: i.e. straightforward calculation of differences between free energies of tautomers as well as between activation energies for the forward and reverse potentially tautomeric reactions. This approach, while not requiring any efforts of chemical imagination, is fraught with practical difficulties and complications associated with the choice of the appropriate methods of quantum mechanical calculations. V. I. Minkin et al. (eds.), Molecular Design of Tautomeric Compounds

Stereochemical Flexibility of Bis(amidomethyl)dichlorogermanes. A Novel Dissociative Mechanism of Ligand Exchange in Neutral Hexacoordinated Bischelate Complexes

“…The relatively high positive entropy of activation in 4 − 6 (Table ) is in accord with a lot of degrees of freedom for the transition state (smaller ordered species) in comparison with the primary state, which may be explained by rupture of the coordination Ge←O bond, forming a pentacoordinate species. It should be noted that a nondissociative mechanism involving the exchange process, for example, through a trigonal-prismatic transition state, characterizes negative entropy of activation 18a and could be ruled out.…”