Photochemical syn-anti isomerization reaction in N-4-hydroxycytosine. An experimental matrix isolation and theoretical study

Infrared spectra of N-4-hydroxycytosine isolated in argon and nitrogen low- temperature matrixes are reported. The compound was found to adopt the syn structure of the imino-oxo tautomeric form exclusively. A photoreaction (la mbda > 250 nm) converting this form into the anti isomer was observed. The reaction is reversible and leads to a photostationary point. The initial in frared spectrum and the spectrum of the photoproduct were assigned to the s yn and anti isomers, respectively. This assignment is based on a close agre ement between the experimental spectra and the spectra theoretically simula ted at the DFT(B3LYP)/6-31++G** level of theory.