Dimethyl 4,5-dichlorobenzene-1,2-dicarboxylate

In the title compound, C10H8Cl2O4, the two Cl atoms and one of the methoxycarbonyl groups are almost coplanar [maximum derivation = 0.035 (2) Å] with the benzene plane, and the other methoxycarbonyl group exhibits an almost orthogonal disposition relative to the benzene plane, with a dihedral angle of 84.82 (3)° between the planes. In the crystal, the molecules are connected into a chain propagating along the [011] direction through nonclassical C—H⋯O hydrogen bonds.

In the title compound, C 10 H 8 Cl 2 O 4 , the two Cl atoms and one of the methoxycarbonyl groups are almost coplanar [maximum derivation = 0.035 (2) Å ] with the benzene plane, and the other methoxycarbonyl group exhibits an almost orthogonal disposition relative to the benzene plane, with a dihedral angle of 84.82 (3) between the planes. In the crystal, the molecules are connected into a chain propagating along the [011] direction through nonclassical C-HÁ Á ÁO hydrogen bonds.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: RK2334).
supplementary materials Acta Cryst. (2012). E68, o834 [doi:10.1107/S1600536812007167] Dimethyl 4,5-dichlorobenzene-1,2-dicarboxylate Yongling Sun Comment Benzenecarboxylate derivatives have been extensively studied due to their excellent chemical properties and easily modified structural natures. (Mallinson et al., 2003 andLiang et al., 2004). Furthermore, the investigate on single-crystal structure of benzenecarboxylate derivatives have become increasingly important in revealing precisely the relation between their chemical properties and molecular structures (Galešić et al., 1984 andRauf et al., 2008). As an extension of our work on benzenecarboxylate structural characterization, the title compound, I, is synthesized and characterized by X-ray diffraction, as shown in Fig. 1.
The compound I crystallizes in the triclinic system and consists of one phenyl framework, together with two chlorine atoms and two methoxycarbonyl groups linked to its peripheral position, respectively. Two chlorine atoms are co-planar with the benzene ring, companying the maximum deviation of 0.035 (2)Å from this benzene plane. Furthermore, one methoxycarbonyl group is also co-planar with this benzene plane, with the dihedral angel of 2.03 (3)° between the methoxycarbonyl plane of C9-O3-O4-C10 and the benzene plane. In contrast, the other methoxycarbonyl plane of C7-O1-O2-C8 exhibits almostly orthogonal configuration in relative to this benzene plane with the dihedral angle of 84.82 (3)° between them. As shown in Table 1

Experimental
To the solution of 4,5-dichloro-1,2-benzenedicarboxyl acid (466 mg, 2 mmol) in MeOH (50 ml), one drop of H 2 SO 4 was added. After refluxed for five hours under N 2 atmosphere, the resulting mixture was evaporated, and the residue was chromatographed on a silica gel column using CHCl 3 as eluent. Repeated chromatography followed by recrystallization

Refinement
All H atoms were placed in geometrically idealized positions and treated as riding on their parent atoms with C-H distances of 0.93Å with U iso (H) = 1.2U eq (C) for aryl H atoms and C-H distances of 0.96Å with U iso (H) = 1.5U eq (C) for methyl H atoms. The CCDC deposit number 863226.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at 30% probability level. H atoms are presented as a small spheres of arbitrary radius. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.24 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 > σ(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.