Infrared spectra of 6-azathiouracils: An experimental matrix isolation and theoretical ab initio SCF/6-311G** study

The infrared (IR) absorption spectra of 2-thio-6-azauracil, 4-thio-6-azauracil and 2,4-dithio-6-azauracil isolated in low-temperature Ar and N-2 matrices are reported. These compounds have been found to exist in low-temperature matrices exclusively in the oxothione and dithione tautomeric forms. An assignment of the observed infrared bands is proposed on the basis of comparison of the experimental matrix spectra with the spectra calculated at the ab initio SCF/6-311G** level. The IR spectra of the title compounds are compared with the previously published IR spectra of matrix isolated 2-thiouracil, 4-thiouracil and 2,4-dithiouracil.