Calculation and Analysis of the IR Spectra of Cytosine in Various Phase States

Plane vibrations and intensities of the IR spectra of the ketone and enol forms of cytosine and deuterocytosine in various phase states are calculated and analyzed. It is shown that in a crystalline state and an aqueous solution cytosine forms a hydrogen bond of two types: C₂=O₈...HN₁ and C₂=O₈...HN₁₀, with a stronger intermolecular interaction in both phases being implemented by the hydrogen bonds between the O₈ and N₁ atoms. A satisfactory interpretation of the spectrum of the isolated molecules of cytosine, with the simultaneously existing ketone and enol tautomeric forms, is possible in the presence of the structural isomers of the enol form that differ in the position of multiple bonds.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 149–156, March–April, 2005.