The experimental electron-density distribution and the distribution of electrostatic potential for 3'-0acetyl-2'-deoxy-5-methyoxymethyluridine have been determined from high-resolution X-ray diffraction data collected at 145 (4) K using graphitemonochromated Mo Ka radiation to sin0/A = 1.08 A. -~ Crystal data: CI3H18N207, Mr = 314.297, triclinic, P1, a= 5.9701 (7), b= 6.7357 (6), c= 9.5770(10) A, a=77.21(1), fl=79.95(1), y= 75.45 (1) °, V= 360.63 (6) A 3, Z = 1, F(000)= 166, D~ = 1.447, Dm = 1.43 (2) Mg m-3, > = 0.]278 mm-~, a = 0.71069 A. The integrated intensities of 15 087 reflections were measured and reduced to 7067 independent reflections with I_> 3o-(1). The partial charges on the atoms of the molecule were determined and are in reasonable agreement with ab initio values reported for fragments of the molecule. The acetal bond, O'(4)--C'(1), shows higher electron density than the O'(4)--C'(4) bond does, which is more typical of an ether bond. The presence within a molecule of methyl H atoms in the vicinity of an O atom that might serve as the acceptor of a hydrogen bond appears to significantly perturb the electrostatic potential around the O atom and make it less acceptable for hydrogen bonding. The atoms N(3), 0(52) and 0(4) combine to create a molecular surface with negative electrostatic potential that extends over part of one face of the 5-methoxymethyluridine ring.
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Wei et al. (1994) studied this question.