2-Oxo-2H-chromen-4-yl propionate

In the title compound, C12H10O4, the atoms of the 2-oxo-2H-chromene ring system and the non-H atoms of the 4-substituent all lie on a crystallographic mirror plane. The molecular structure exhibits an intramolecular C—H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, molecules form R 3 2(12) trimeric units via C—H⋯O interactions which propagate into layers parallel to the ac plane. These layers are linked by weak C—H⋯O interactions along the [010] direction, generating a three-dimensional network.

In the title compound, C 12 H 10 O 4 , the atoms of the 2-oxo-2Hchromene ring system and the non-H atoms of the 4substituent all lie on a crystallographic mirror plane. The molecular structure exhibits an intramolecular C-HÁ Á ÁO hydrogen bond, which generates an S(6) ring. In the crystal, molecules form R 3 2 (12) trimeric units via C-HÁ Á ÁO interactions which propagate into layers parallel to the ac plane. These layers are linked by weak C-HÁ Á ÁO interactions along the [010] direction, generating a three-dimensional network.
They found applications in cosmetic and food industries (O′Kennedy & Thornes, 1997) and are also potential laser dyes (Lakshmi et al., 1995). Owing its versatile properties, coumarin ring system has become a hub nucleus in the developing of new molecules in organic, medicinal and material chemistry. We have synthesized novel coumarin derivatives substituted at position 4 in order to explore the new properties of this compound class. Herein, we report single-crystal structure of title compound.
The molecular structure of title compound (and its atomic numbering scheme) is illustrated in Fig. 1. As expected, the coumarin moiety is planar as shown in the recent X-ray diffraction analysis of 4-substituted coumarin derivative (Abou et al., 2012). Analysis of bond length values of aromatic ring indicate the existence of a delocalized π-electron cloud in this one. In this structure, except the H atoms of the substituent groups, all other atoms lie in a crystallographic mirror plane (x, y = 1/4, z). We also note the existence of an intramolecular C-H···O hydrogen bond which generates a S(6) ring motif (Bernstein et al., 1995).
In the three-dimensional crystal packing, molecules form cyclic trimers of R 3 2 (12) motifs (Bernstein et al., 1995) via two independent intermolecular C-H···O hydrogen bond interactions along the a axis (Fig. 2). These trimolecular aggregates propagate into parallel layers to the ac plane (Fig. 3). These layers are additionally stabilized by weak intermolecular C-H···O interactions along [010] direction.

Experimental
To a solution of propionic chloride (125 mmol) in dried diethyl ether (300 ml) was added dried pyridine (4 ml) and 4-hydroxycoumarin (120 mmol) in small portions over 30 min. The mixture was then refluxed for 3 h and poured in 300 ml of chloroform. The solution was acidified with dilute hydrochloric acid until the pH was 2-3. The organic layer was extracted, washed with water, dried over MgSO 4 and the solvent removed. The crude product was recrystallized from acetone. Colourless single crystals of the title compound were obtained in a good yield: 69.7%; m.p. 358-359 K.

Refinement
The structure solution program SIR2004 (Burla et al., 2005) was used to solve the structure. The .res file shows that all non H atoms lie on special positions (x, 1/4, z) with a site-occupancy factor of 0.5. As the program SHEIXL97 (Sheldrick, 2008) will automatically work out and apply the appropriate positional, s.o.f. and U ij constraints for any special positions, we have not refined these non H atoms parameters with further constraints. However, omitted from the refinement supplementary materials because of bad disagreements were (7 0 4), (7 2 4), (4 1 1), (1 0 1), (0 0 2).
H atoms were placed in calculated positions [C-H = 0.93 (aromatic), 0.96 (methyl group) or 0.97 Å (methylene group)] and refined using a riding model approximation with U iso (H) constrained to 1.2 (aromatic and methylene group) or 1.5 (methyl group) times U eq of the respective parent atom.

Figure 1
The molecular structure of the title compound and the atomic numbering scheme.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.16 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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. The DENZO image processing package used during process data may have problems with certain strong reflections. These reflections are often excluded from the data set to result in _diffrn_measured_fraction_theta_full Low (0.974 in our nvestigation study). However, it presents no problem in the refinement since the data-to-parameter ratio is superior to 10. In the initial refinement, extinction correction (EXTI) has been applied because SHELXL has suggested it; but in the last cycles of the refinement, the EXTI instruction has been removed because of PLATON checkCIF reports mentioning extinction parameter within range (2.20 σ). The non H atoms lie in the miror plane at y = 1/4. Therefore the U ij constraints (U 12 = U 23 = 0) generated automatically by SHELXL for this special positions (x, 1/4, z) in the space group Pnma is responsible for the elongated thermal ellipsoids in the [010] direction causing a large U 3 /U 1 ratio for the average U(i,j) tensor (2.4). The low U eq as compared to neighbors for atom C10 may be caused by the carbonyl bond in which the oxygen atom vibrates more than the carbon atom (Braga & Koetzle, 1988). Moreover, the decrease of U eq from C12 to C10 of the propanoate substituent originates from the minor unresolved disordered H atoms bonded to the non disordered carbon atom C12 (split H atoms) revealed by manual inspection of PLATON (Spek, 2009)