Molecular structure of 6-methyluracil in the gas phase and characteristics of the 6-methyluracil-water system

Geometric parameters of the 6-methyluracil molecule were determined by gas-phase electron diffraction: interatomic distances (ra, Å) N1-C2 1.390(3), C2-N3 1.384(3), N3-C4 1.407(3), C4-C5 1.455(10), C5-C6 1.336(20), C1-C6 1.395(3), C-Me 1.519(5); bond angles (deg) N1C2N3 114.1(), C2N3C4 126.3(7), N3C4C5 114.3(5), C4C5C6 121.6(5), C5C6C1 119.7(5), C7C6C5 11C5.4(8), O8C2N1 123.5(1.5), O9C4N3 123.3(10). The heterocycle is planar. One of the C-H bonds of the methyl group and the C5=C6 bond are coplanar. The nearest surrounding of the heterocycle by water molecules (four and five molecules) was examined by AM1 and B3LYP/6-31G** calculations, and the energies of the hydrogen bonds in the heterocycle-water system were estimated.