Abstract
6-Methyluracil, C5H6N2O2, exists in two crystalline phases: form (I), monoclinic, space group P21/c [Reck et al. (1988). Acta Cryst. A44, 417–421] and form (II), monoclinic, space group C2/c [Leonidov et al. (1993). Russ. J. Phys. Chem. 67, 2220–2223]. The structure of polymorph (II) has been redetermined providing a significant increase in the precision of the derived geometric parameters. In the crystal, molecules form ribbons approximately running parallel to the c-axis direction through N—H...O hydrogen bonds. The radical differences observed between the crystal packing of the two polymorphs may be responsible in form (II) for an increase in the contribution of the polar canonical forms C—(O−)=N—H+ relative to the neutral canonical form C(=O)—N—H induced by hydrogen-bonding interactions.
Highlights
6-Methyluracil, C5H6N2O2, exists in two crystalline phases: form (I), monoclinic, space group P21/c [Reck et al (1988)
The radical differences observed between the crystal packing of the two polymorphs may be responsible in form (II) for an increase in the contribution of the polar canonical forms C— (OÀ) N—H+ relative to the neutral canonical form C( O)—N—H induced by hydrogen-bonding interactions
As a result of the fundamental role of nucleic acids in genetic processes of living systems, much attention has been devoted to determining the structure of methylated derivatives of uracil, because methylation of DNA is probably involved in various genetic alterations and in the initiation of carcinogenic processes
Summary
CCDC reference: 1924198 Structural data: full structural data are available from iucrdata.iucr.org. 6-Methyluracil, C5H6N2O2, exists in two crystalline phases: form (I), monoclinic, space group P21/c [Reck et al (1988). A44, 417–421] and form (II), monoclinic, space group C2/c [Leonidov et al (1993). The structure of polymorph (II) has been redetermined providing a significant increase in the precision of the derived geometric parameters. Molecules form ribbons approximately running parallel to the c-axis direction through N—HÁ Á ÁO hydrogen bonds. The radical differences observed between the crystal packing of the two polymorphs may be responsible in form (II) for an increase in the contribution of the polar canonical forms C— (OÀ) N—H+ relative to the neutral canonical form C( O)—N—H induced by hydrogen-bonding interactions
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