Analysis of Real Tautomeric Systems

In the early days of spectroscopy, Dobbie et al. [6] introduced the so-called model compounds whose spectra might be used in Eq. (2.2) instead of the missing spectra of the individual tautomers. In these compounds, the tautomeric proton is replaced by a Me group, whose weak electronic effect leads to only a minor spectral shift in planar tautomeric systems. For this reason, model compounds have been extensively used for quantitative analysis in heterocyclic tautomers, assuming that (i) molar absorptivity of the model tautomer and of the real tautomer are equal at their absorption maxima, and (ii) neglecting that these absorption maxima could be shifted [7]. From Table 2.1, where the predicted spectral characteristics of some real and fixed tautomers are collected, it is obvious that these assumptions are reasonable in the case of 1. 

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