trans-Cyclohex-2-ene-1,4-diyl bis(4-nitrophenyl) dicarbonate

Although the title molecule, C20H16N2O10, does not possess molecular inversion symmetry, it lies on a crystallographic inversion centre which imposes disorder on the central cyclohexene ring. In addition, the cyclohexene ring has non-symmetry-related disorder over two sites, with the ratio of the major and minor components being 0.54:0.46. The overall effect is to produce four disorder components for the atoms of the cyclohexene ring. The side chain is perfectly ordered and the dihedral angle between the atoms of the carbonate group (O=CO2—) and the benzene ring is 72.99 (6)°.

Although the title molecule, C 20 H 16 N 2 O 10 , does not possess molecular inversion symmetry, it lies on a crystallographic inversion centre which imposes disorder on the central cyclohexene ring. In addition, the cyclohexene ring has nonsymmetry-related disorder over two sites, with the ratio of the major and minor components being 0.54:0.46. The overall effect is to produce four disorder components for the atoms of the cyclohexene ring. The side chain is perfectly ordered and the dihedral angle between the atoms of the carbonate group (O CO 2 -) and the benzene ring is 72.99 (6) .

Comment
The title compound, (I), was synthesized two decades ago (Fréchet et al., 1986) as a mixture of cis and trans isomers starting with a cis and trans mixture of cyclohex-2-ene-1,4-diol to obtain electrophilic character of diols. This compound has been used to obtain a wide variety of thermally and acid labile polymers for a variety of applications (Fréchet et al., 1987;Ericsson & Hult, 1991). We have used the trans isomer of this alcohol for the synthesis of a number of homo and copolycarbonates (Ali et al., 2008).
We report here the crystal structure of (I). Figures 1 and 2 show the two non-symmetry related components of disorder for the cyclohexene ring in (I). The crystallograhic inversion related disorder is not shown.

Experimental
A solution of 4-nitrophenylchloroformate (1.41 g, 7.0 mmol) in dry dichloromethane (20 ml) was added dropwise via a 100 ml separating funnel into a solution of cyclohex-2-ene-1,4-diol (trans isomer) (0.40 g, 3.5 mmol) in anhydrous pyridine (0.49 g, 0.5 ml, 6.2 mmol) and dry dichloromethane (10 ml) in a 100 ml round-bottom flask. A white suspension appeared which was allowed to stir gently at room temperature for 12 h. After this time more dry dichloromethane (25 ml) was added, which dissolved the suspension and then the reaction mixture was stirred for another 6 h. Then it was quenched by adding deionized water (30 ml). The reaction mixture was transferred to a separating funnel (250 ml), and the lower organic phase was removed. The aqueous phase was washed with dichloromethane (20 ml × 2), and all the dichloromethane solutions were combined. These were then washed with deionized water (20 ml × 2), a 1.0% solution of acetic acid (30 ml × 2) and once more with deionized water (25 ml × 2), and then dried over anhydrous magnesium sulfate and filtered. After filtration, the solvent was removed by rotary evaporation. The product was dried in air overnight in a fume hood and then in a vacuum oven for 24 h at room temperature (< 1 Torr). The desired product was obtained in good yield (1.35 g, 86.5%) as a white crystalline solid. The product was recrystallized in dichloromethane and colourless needles of (I) were obtained by slow evaporation of solvent at room temperature. In addition to the X-ray structure determination, the structure of the crystalline sample was confirmed by Mass and NMR ( 1 H and 13 C)Spectroscopy.

Refinement
All the hydrogen atoms were placed in calculated positions with C-H = 0.95 − 1.00 Å and refined as riding with U iso (H) = 1.2U eq (C). The components of the two symmetry independent disorder sites refined to 0.2680 (13) and 0.2320 (13). The disorder was modelled by creating two full rings for each component and by using suitable constraints and restraints to give each ring component similar geometries.

Special details
Geometry. All e.s. 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 > 2sigma(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.