Keto-Enol Tautomerism in 4- phenyldiazenyl naphthalen-l-ol Solvent Effect

Keto-Enol Tautomerism in 4-(phenyldiazenyl)naphthalen-l-ol Solvent Effect 

4-(Phenyldiazenyl)naphthalen-l-ol (2) is one of the first tautomeric compounds discovered [39] and, in spite of its limited practical applicability, is one of the most studied [40]. Its attractiveness is due to the lack of intramolecular hydrogen bonding, as for instance, in 4, which makes the tautomeric equilibrium very sensitive to changes in the solvent environment. Hence, this compound is a suitable model, as shown in Chapters 11 and 13, to test the description of solvent effects both theoretically and experimentally. At the same time, the shift in the position of the equilibrium, caused by the temperature, is, in most solvents, very small slight and relatively difficult to be processed [13]. 

The logical algorithm, which is applied in this case includes the following steps [26]  

Assignment of each individual band to one of the tautomeric forms according to the following principle the increase in the content of the tautomer 2a with increasing water content leads to an increase of the areas of the individual bands. 

10) The infoiTTiation for the nmnber of individual bands comes from derivative spectroscopy (second and fourth order), but the possibility for assignment of each band to one of the tautomeric forms (next step in the logir l algorithm) serves as additional tool for the estimation of n. 

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