5-Fluoro-1-(pentanoyl)pyrimidine-2,4(1H,3H)-dione

The pentanoyl group and the 5-fluorouracil moiety of the title compound, C9H11FN2O3, are essentially coplanar, with the pentanoyl carbonyl group oriented towards the ring CH group and away from the nearer ring carbonyl group. In the crystal structure, two inversion-related molecules form a dimer structure, in which two N—H⋯O hydrogen bonds generate an intermolecular R 2 2(8) ring. In addition, there are intra- and intermolecular C—H⋯O interactions.

The pentanoyl group and the 5-fluorouracil moiety of the title compound, C 9 H 11 FN 2 O 3 , are essentially coplanar, with the pentanoyl carbonyl group oriented towards the ring CH group and away from the nearer ring carbonyl group. In the crystal structure, two inversion-related molecules form a dimer structure, in which two N-HÁ Á ÁO hydrogen bonds generate an intermolecular R 2 2 (8) ring. In addition, there are intra-and intermolecular C-HÁ Á ÁO interactions.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: AT2544).
The molecular structures of the title compound and the other 1-acyl-5-fluorouracil derivatives are very similar.
Specifically, the 1-acyl group and the 5-fluorouracil moiety are almost coplanar, with the C7?O7 carbonyl group oriented towards the C6-H group and away from the C2?O2 group in all four crystal structures. The C6-N1-C7-O7 dihedral angle of all 1-acyl-5-fluorouracil derivatives is comparable and ranges from 1.6 to 17.3° (Beall et al., 1997;Jiang et al., 1988;Lehmler & Parkin, 2000). In the crystal structure, two inversion-related molecules form a dimer structure, in which two N-H···O hydrogen bonds generate an intermolecular R 2 2 (8) ring. In addition, there are C-H···O type-intra and intermolecular interactions.

S3. Refinement
H atoms were found in difference Fourier maps and subsequently placed in idealized positions with constrained C-H distances of 0.98 Å (RCH 3 ), 0.99 Å (R 2 CH 2 ), 0.95 Å (C Ar H) and 0.88 Å (NH) with U iso (H) values set to either 1.2U eq or 1.5U eq (RCH 3 only) of the attached atom.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.23 e Å −3 Δρ min = −0.24 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.