“…This may be attributed to the long-range e †ect of the substitution of N for CH in position 5 compared to uracil and 6-azauracil, and is slightly more marked in 5azauracil hydrate. As a point of interest the stretching of the N1wC2 bond in 5-azauracil hydrate to 1.3847 (9) agrees Ó well with the value of 1.384 assigned from a theoretical Ó CNDO2 study. 29 The O2xC2 carbonyl bond length in 5- azauracil is noticeably shorter than O4xC4, a reversal of the situation in the 5-azauracil complex structure.…”