Structure and conformation of 5-bromo-2',3'-dideoxyuridine.

C9H11BrN2O4, Mr = 291.11, monoclinic, P2(1), a = 11.307 (1), b = 5.954 (1), c = 15.829 (2) A, beta = 93.25 (1) degree, V = 1063.90 A3, Z = 4, Dx = 1.82 g cm-3, lambda(Cu K alpha) = 1.54184 A, mu = 53.58 cm-1, F(000) = 584, T = 295 K, R = 0.034 for 1927 observed reflections [I greater than 3 sigma(I)]. The crystal structure contains two independent molecules forming a dimer linked by a pair of N3--H...O2 hydrogen bonds; the crystal structure is stabilized by four additional hydrogen bonds. Two of these are internal C6--H6...O5' hydrogen bonds, one in molecule A and another in molecule B. These two molecules exhibit two different conformations; their sugar ring puckers are 2'-endo-3'-exo for molecule A and 3'-endo-2'-exo for molecule B. The Cl'--N1 distance, the chi CN torsion angle and the glycosidic conformation are 1.464 (8) A, -130.0 degrees and -anticlinal for molecule A and 1.506 (8) A, -168.9 degrees and -antiperiplanar for molecule B, respectively.