Tautomerism Suppl

The Tautomerism of Heterocycles J. Elguero etal., Adv. Heterocycl. Chetn., Suppl. 1,1976. Ring-Chain Isomeric Transformations of Hydroxy-, Amino-, and Mercapto-Derivatives of Carbonyl Compounds and Their Heteroanalogues R. Valters, Russ. Chem. Rev. Engl. Transl.), 1974, 43, 665-678. 

Books sometimes disagree on the preferred tautomer of guanine—6.f versus 6.g. A parallel can be found in 2-pyridone, which also has two likely tautomeric forms, 6.h and 6.i. To determine which form of 2-pyridone predominates, the ultraviolet spectra of two isomers, l-methyl-2-pyridone (6.j) and 2-methoxypyridine (6.k), were obtained with the observed Amax wavelengths shown. The Amax of 2-pyridone is at 229 nm. Does 2-pyridone likely favor tautomer 6.h or 6.i Which tautomer of guanine is likely favored, 6.f or 6.g (Elguero, J., Marzin, C., Katritzky, A. R., Linda, P. The Tautomer-ization of Heterocycles. Adv. Heterocycl. Chem., Suppl. 1 New York Academic Press, 1976.)... 

In contrast with the hydroxy compounds, comparatively little is known of the tautomeric preferences of pyrrole- and indole-thiols. The compounds are readily oxidized to form the bis-heteroaryldisulfides and the available spectral data fpx the monomeric systems suggest that, in contrast with the oxygen analogues, the 2-pyrrole- and 3-indole-thiols exist predominantly as such, whereas the sulfur analogue of oxindole is the predominant tautomer for the 2-indolyl system <63AHC(2)1, 76AHC(Suppl. 1)214). 

J. Elguero, C. Marzin, A. R. Katritzky, and P. Linda, The Tautomerism of Heterocycles, Adv. Heterocycl. Chem., Suppl. 1. Academic Press, New York, 1976. 

Prototropic Tautomerism-Five-Membered Rings with One Hetero Atom Suppl. 1,1976, 214-265 ... 

---