Crystal structure of 3-bromoacetyl-6-chloro-2H-1-benzopyran-2-one

In the title compound, C11H6BrClO3, the benzopyran ring system is essentially planar, with a maximum deviation of 0.036 (2) Å for the O atom. The Cl and Br atoms are displaced by −0.0526 (8) and 0.6698 (3) Å, respectively, from the mean plane of this ring system. In the crystal, two pairs of weak C—H⋯O hydrogen bonds to the same acceptor O atom link molecules into inversion dimers.

There are two polymorphic forms of 3-acetyl coumarin reported (Munshi et al., 2004;Munshi et al., 2006). In both cases the structure directing interactions are weak C-H···O hydrogen bonds. In one form (Munshi et al., 2004), a sheetlike structure is formed with two independent molecules in the asymmetric unit and in other form (Munshi et al., 2006) the supramolecular assembly is formed via inter-penetrating sheets with one molecule in the asymmetric unit and contains inversion dimer units connected through weak C-H···O interactions. With the substitution of bromine and chlorine (Chopra et al., 2006;2007a,b) in 3-acetyl coumarin there is no significant differnce in the packing and type of weak interactions. In the crystal of the title compound, pairs of bifurcated -(C-H) 2 ···O hydrogen bonds form inversion dimers. The molecular structure of the title compound is shown in Fig. 1.
The solid was washed with ether and crystallized from glacial acetic acid to yield 3-bromoacetyl-6-chloro-2H-1-benzopyran-2-one. Needle shape crystals were obtained by dissolving the title compound in glacial acetic acid and warming for a few minutes in a 10ml beaker. The beaker was covered with paraffin film with few holes in it and left till crystals appeared.

S3. Refinement
All H atoms were positioned geometrically and refined using a riding-model approximation with C-H = 0.93 or 0.97 Å and U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of the title compound with displacement ellipsoids for non-H atoms drawn at the 50% probability level.

Figure 2
The reaction scheme. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.43 e Å −3 Δρ min = −0.60 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.