[Investigation of tautomeric composition of cytosine by multiphoton excitation spectra. I. Resonance hyper-Raman spectra].

For the first time the quantum-mechanical calculations of intensity distribution in the resonance hyper-Raman spectra of the six tautomeric forms of cytosine were performed. It has been confirmed that in the aqueous solution of cytosine (pH 3.0) there exist several molecular structures: cytosine in the canonical amino-oxo tautomeric form, cation, as well as cys-imino-oxo and cys-amino-hydroxy tautomers; in the gaseous phase at 235 degrees C cys-imino-oxotautomer dominates with the presence of small amount of cys-, trans-, amino-hydroxy tautomers and the caconical form of cytosine.