4-Bromomethyl-7-methyl-6,8-dinitrocoumarin

The crystal structure of the title compound, C11H7BrN2O6, establishes the substitution positions of the nitro groups from the nitration reaction of 7-methyl-4-bromomethyl coumarin. The mean planes of the nitro groups form dihedral angles of 43.9 (8) and 52.7 (10)° with the essentially planar [maximum deviation 0.031 (6) Å] benzopyran ring system.


Related literature
For background information on the nitration of coumarin compounds, see: Kulkarni et al. (1983); Clayton et al. (1910). For a related structure, see: Vasudevan et al. (1990). For ab initio calculations on 6-methyl-4-bromomethylcoumarins, see: Sortur et al. (2006). KVAG gratefully thanks the DST for financial support through the SERC Fast Track Young Scientists Scheme and RG thanks MVJ College of Engineering Bangalore (Reasearch Center). The authors also thanks Professor T. N. Guru Row, Chairman, SSCU IISc, Bangalore, for the X-ray data collection.

S1. Comment
The molecular structure of the title compound is shown in Fig. 1. The bromomethyl group is twisted is out of the plane of the benzopyran ring as described by the torsion angle of 104.6 (7)° for C2-C3-C10-Br. This is in agreement with the ab initio calculations on 6-methyl-4-bromomethylcoumarins (Sortur et al., 2006). Positions C-6 and C-8 (refers to positions from systematic naming scheme) become activated due to the electron donating methyl group at C-7 and hence nitration occurs at C-6 and C-8 consistent with the title compound which is also in agreement with earlier reports (Clayton, 1910;Kulkarni et al., 1983).

S2. Experimental
5.06 g of 7-methyl-4-bromomethyl coumarin (0.02 mol) was dissolved in conc. sulfuric acid (10 ml) and treated with a nitrating mixture 15 ml (10 ml H 2 SO 4 + 5 ml HNO 3 ) at ice bath temperatures (273-278K). The reaction mixture was then allowed to stand at room temperature for two hours and the reaction mixture was poured over crushed ice. The separated solid was washed with excess of water, dried and recrystallized from glacial acetic acid. Crystals suitable for diffraction studies were grown by slow evaporation of an ethanol solution of the title compound.

S3. Refinement
Hydrogen atoms were positioned geometrically with C-H = 0.93-0.97 A° and included in the refinment in a ridingmodel approximation with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C) for methyl C atoms.  The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atomic numbering.

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 > 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.