Methods to Distinguish Tautomeric Cases from Static Ones

Methods to Distinguish Tautomeric Cases from Static Ones 

Tautomerism may be of many kinds as illustrated in this book and in Ref. [1]. However, tautomerism may be less obvious depending on the rates of interconversion or the equilibrium constant may be very much in favor of one form. A typical example of the latter is acetone and other ketones. Nevertheless, tautomerism plays a major role in the chemistry of alkyl ketones. Tautomerism may occur both in the gas phase, namely the liquid and condensed phases, and in the solid state, namely in the ground state as well as in the excited state. As tautomerization often involves the movement of light atoms, proton transfer is the usual case and hydrogen bonding will often be involved. Tautomerization can of course be both intra- and intermolecular, and in the latter case a solvent molecule may also be involved. For some characteristic cases, see Ref. [1, Chapter 3]. 

This chapter will provide an overview as well as provide tools by discussing different techniques either individually or in combination, in order to achieve the often difficult goal of disclosing tautomerism in new types of compounds. 

The techniques considered are UV, NMR, isotope effects on chemical shifts. Infra Red spectroscopy, fluorescence, density functional theory (DFT) calculations, and X-ray as well as analytical techniques such as principal component analysis and fishing algorithms. Theoretical calculations will be treated in a number of cases such as energy differences of the two forms, calculations of chemical shifts of tautomeric species, calculation of isotope effects on chemical shifts including new and promising methods, calculation of IR vibrational frequencies, and a discussion of strongly hydrogen bonded cases. 

Many other techniques have clearly been used over time. Some are very relevant in some cases like small molecules although not in others. 

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I 3 Methods to Distinguish Tautomeric Cases from Static Ones... 

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