CRYSTAL STRUCTURE AND PHOTOCHEMISTRY OF 5-AZACYTOSINE: EXPERIMENTAL AND THEORETICAL STUDY.

The crystal structure of 5-azacytosine was proposed by the X-ray diffraction pattern of the compound and the performed Rietveld analysis. The crystal structure solutions were achieved with the simulated annealing procedure. The model molecule for the procedure was taken from the BLYP/aug-cc-pVDZ optimization of the N1(H) oxo-amino tautomer of the compound. The refined unit cell parameters are: a = 12.82916 Å, b = 9.47282 Å, c = 3.66363 Å, and space group P212121. The studied excited-state reaction paths of the H-detachment processes of two oxo-amino tautomers show a possibility for mutual phototransformation of the two oxo-amino tautomers: N1(H) and N5(H). The driven states of this photoreaction are the 1nσ* and 1πσ* excited states. [ABSTRACT FROM AUTHOR]