PHOTOCHEMICAL GENERATION OF RARE DITHIOL FORM OF 2,4-DITHIOURACIL

Abstract

2,4-Pyrimidinedithiol - the ``rare'' dithiol tautomer of 2,4-dithiouracil - was obtained in low-temperature Ar and $N_{2}$ matrices by UV ($\lambda > 335$ nm) irradiation of 2,4-dithiouracil (existing initially exclusively in its dithione tautomeric form). This is the first observation of the ``rare'' tautomeric form of any uracil analogue. The identification of the photoproduct was based on the good agreement between the experimental IR absorption spectrum and the spectrum theoretically predicted at the DFT(B3-LYP)/6-31G(d,p) level. The observed photoreaction represents the first case of intramolecular photoinduced double proton transfer of the type entirely different from the known ESIPT (Excited State Intramolecular Proton Transfer) processes.