FT-IR SPECTROSCOPIC STUDY OF URACIL DERIVATIVES AND THEIR HYDROGEN-BONDED COMPLEXES WITH PROTON DONORS .3. HYDROGEN-BONDING OF URACILS WITH H2O IN ARGON MATRICES

The hydrogen bond interaction of uracils (uracil, 1-CH3-uracil, 3-CH3-uracil, 5-CH3-uracil, 1,3-diCH3-uracil) and thiouracils (2-thiouracil, 4-thiouracil, 1-CH3-2-thiouracil, 1-CH3-5-Br-2-thiouracil) with water is investigated using matrix-isolation FT-IR spectroscopy. It is demonstrated that H2O forms both C = O...H-O and N-H...O-H complexes in low temperature Ar matrices. No experimental evidence is obtained for the existence of a closed C = O...H-O...H-N heterodimer which has been predicted from ab initio calculations. Different amounts of C2O and C4O, and of N1H and N3H complexes are formed in the matrix depending on the substitution (methyl, thio, halogen) on the uracil ring. The monomer assignments in earlier reports are supported by the shifts observed on H-bonding with H2O.