Infrared spectra carbinolamines

These structural problems are also insoluble by physical methods alone. The infrared spectrum often gives an unambiguous decision about the structure in the solid state the characteristic bands of the carbonyl or the hydroxyl group decided whether the compound in question is a carbinolamine or an amino-aldehyde. However, tautomeric equilibria occur only in solution or in the liquid or gaseous states. Neither infrared nor ultraviolet spectroscopy are sufficiently sensitive to investigate equilibria in which the concentration of one of the isomers is very small but is still not negligible with respect to the chemical reaction. 

The behavior of the 1 -methiodide (179) is more difficult to explain as its spectrum in alcohol is nearly identical to that in alkaline solution, and these both show the same pattern as the 2-methylene indoline, i.e., with an intensified band II and a band III shifted to the red as compared to its methiodide. It seems possible that these compounds exist as the carbinolamine, or pseudobase, in hydroxylic solvents and are in tautomeric equilibrium (179 181). The direction of this equilibrium has been attributed by Beke to the basicity of the nitrogen, as well as other factors. B14ha and Cervinka discuss the importance of steric and polar structural factors, citing examples of stable pyrrolidine pseudobases. Indeed, Ficken and Kendall isolated the 4-azaindoline pseudobase (123), characterizing it by analysis and infrared spectral evidence. They similarly characterized the 2-methylene base (121), and it is unfortunate that their ultraviolet spectra were not determined. The 2-methylene-7-azaindoline... 

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