Fourier-transform infrared spectroscopic study of uracil derivatives and their hydrogen-bonded complexes with model proton donors .7. 3-methyl-2-thiouracil and its complexes in argon matrices - substituent effect on characteristic uracil frequencies
3-Methyl-2-thiouracil (3M2SU) was synthesized and isolated in low-temperature argon matrices which were either pure or doped with H2O or HCl. Details of the IR spectrum of the monomeric compound are reported and compared with earlier matrix and recent literature data for a large series of other uracils. A full description of the effect of substitution on characteristic uracil frequencies is presented. Hydrogen bonding of 3M2SU with H2O or HCl occurs at the C4 = O lone pairs, but small amounts of N1-H...X-H species are also detected. Self-association takes place through C4 = O...H-1N hydrogen bonding in 1:1 or higher stoichiometry complexes, depending on the deposition and annealing conditions applied. All the experimental data fit in fairly well with earlier reported spectral characteristics for complexes of uracils and thiouracils.