9,10-Dimethyl-9,10-peroxy-9,10-dihydroanthracene

The structure of the title compound, C16H14O2, contains one half-molecule in the asymmetric unit and the molecule is located on a mirror plane. The dihedral angle between the two benzene ring planes is 53.07 (6)°. The crystal structure involves intermolecular C—H⋯O hydrogen bonds.

The structure of the title compound, C 16 H 14 O 2 , contains one half-molecule in the asymmetric unit and the molecule is located on a mirror plane. The dihedral angle between the two benzene ring planes is 53.07 (6) . The crystal structure involves intermolecular C-HÁ Á ÁO hydrogen bonds.

Comment
The Friedel-Crafts reaction of an alkyl halide with an aromatic hydrocarbon in the presence of aluminium chloride yields a substituted phenyl compound (Price, 1946). The reaction does not, however, stop at the stage of mono-substitution, an unpredictable compound was reported and determined by X-ray crystal structure analysis. The molecule of the title compound lie on a crystallographic mirror plane, which pass through atoms C1/O1/O2/C8/C9/C10 (Fig. 1). The geometrical parameters for (1) are similar to those of related 9,10-bridged anthracene derivatives (Simpson et al., 2004;Gable et al., 1996;Burrows et al., 1999). Atoms C1, C8 are almost coplanar with the benzene ring plane, and the deviating distance from the benzene ring are 0.0074 Å, −0.066 Å respectively. The dihedral angle between the plane of bridge atoms C1-O1-O2-C8 and the benzene ring plane is 63.45 (5)°. The benzene ring plane and its symmetry-related one form the dihedral angle of 53.07 (6)°, which is smaller than that of 9,10-bridged anthrancene systems, e.g. the corresponding dihedral angle in 11,12bis(N,N-dimethyl-aminomethyl)-9,10-dihydro-9,10-ethanoanthrancene (Karolak-Wojciechowska et al., 1998) is 58.8 (2)°.
The three six-membered rings of the bicycle core of (1) , link the molecules into circles (Fig. 2). The bridged O2 atom attached to H4 atom of neighbouring benzene ring may result in the longer distance O2-C8, compared with the bond length C1-O1 (Table 1).

Experimental
Ethyl 2-bromo-2-methylpropionate (3.84 g, 20 mmol) was added to a 50 ml flask equipped with a reflux condenser and large magnetic stirrer. Anhydrous benzene (20 ml) was added to the flask, followed by fresh anhydrous AlCl 3 (9.00 g, 67.5 mmol) in small portions. The solution was then slowly heated to the reflux temperature and at this time the exit of the reflux condenser was connected to a flowing-water HBr trap. The mixture was heated a total of 24 h without interruption. The reaction mixture was then cooled to 278k. and treated with 20 ml of 50/50 (by volume) conc. HCl/H 2 O to decompose the catalyst complex. The benzene layer was then separated, washed once with ice-cold H 2 O (12 ml) and twice with dilute aqueous sodium hydroxide. The organic phase was evaporate. After 6 days, a single-crystal suitable for X-ray analysis was obtained by recrystallization from ethanol.

Refinement
All H atoms were placed in calculated positions with C-H = 0.93-0.96 Å and included in the refinement in riding model, with U iso (H) = 1.2U eq (carrier atom). In the absence of anomalous scatterers, no attempt was made to establish the absolute configuration of the title compound. 9,10-Dimethyl-9,10-peroxy-9,10-dihydroanthracene

Special details
Refinement. Refinement using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0σ(F 2 ) is used only for calculating R-factor (gt).
Data collection(812 indenpent reflections but 699 in refinement): The author of the software, Dr Lee Daniels (ldaniels@RigakuMSC.com) explain this problem (see following). The number of reflections used to refine the cell is taken from the diffractometer program, which uses all available reflections measured in different scans. Even though some reflections are used more than once, they measured at different psi angles and therefore represent independent observations for determination of the cell dimensions.