Allyl 4-hydroxyphenyl carbonate

The title molecule, C10H10O4, is a functionalized carbonate used in the synthetic route to organic glasses. The central CH fragment of the allyl group is disordered over two positions, with occupancies in a 0.758 (10):0.242 (10)ratio. This disorder reflects the torsional flexibility of the oxygen–allyl group, although both disordered parts present the expected anticlinal conformation, with O—CH2—CH=CH2 torsion angles of −111 (2) and 119.1 (4)°. The crystal structure is based on chains parallel to [010], formed by O⋯H—O hydrogen bonds involving hydroxyl and carbonyl groups as donors and acceptors, respectively. The molecular packing is further stabilized by two weak C—H⋯π contacts from the benzene ring of the asymmetric unit with two benzene rings of neighboring molecules.

The title molecule, C 10 H 10 O 4 , is a functionalized carbonate used in the synthetic route to organic glasses. The central CH fragment of the allyl group is disordered over two positions, with occupancies in a 0.758 (10):0.242 (10)ratio. This disorder reflects the torsional flexibility of the oxygen-allyl group, although both disordered parts present the expected anticlinal conformation, with O-CH 2 -CH CH 2 torsion angles of À111 (2) and 119.1 (4) . The crystal structure is based on chains parallel to [010], formed by OÁ Á ÁH-O hydrogen bonds involving hydroxyl and carbonyl groups as donors and acceptors, respectively. The molecular packing is further stabilized by two weak C-HÁ Á Á contacts from the benzene ring of the asymmetric unit with two benzene rings of neighboring molecules.

Comment
We have synthesized some functionalized aromatic allyl ester (Herrera et al., 2003) and allyl carbonate compounds (Herrera, 2006) as intermediates in the preparation of new diallylcarbonate monomers, which are potential precursors of organic glasses. One representative example is the title molecule, which includes phenol and allyl functional groups as substitutents of the carbonate core (Fig. 1).
The allyl group presents a degree of flexibility, resulting in two disordered positions for the methylene group, C21 and C22, with site occupation factors 0.758 (10) and 0.242 (10), respectively ( Fig. 1, inset). Regardless of the position for the CH 2 fragment, O-allyl chain displays the expected anticlinal conformation, characterized by torsion angles O-CH 2 -CH═CH 2 of -111 (2)° and 119.1 (4)°. A similar disorder was previously observed for a closely related phenol allylic derivative, allyl-4-hydroxybenzoate (Herrera et al., 2003). To date, only two acyclic allyl carbonate systems have been X ray characterized, both with non disordered allyl groups. The anticlinal conformation has been stabilized in the first molecule, with O-allyl torsion angle of -131.4° (Michelet et al., 2003), while in the most recent report, a synperiplanar O-allyl group is observed, the torsion angle being 9.7° (Burns & Forsyth, 2008). This very limited set of structurally characterized allyl carbonate derivatives does not allow to determine the factors influencing the stable conformation for these molecules in the solid state. In contrast, a number of allyl ester derivatives have been X-ray characterized, with conformations restricted to two attractors (Herrera et al., 2003).
The crystal structure of the title compound is based on chains running along [010], formed through O···H-O bonds, where carbonyl functionalities act as acceptor and hydroxyl functionalities as donor groups. Moreover, two aryl C-H groups of the benzene ring of the asymmetric unit form stabilizing C-H···π contacts with the centroids of two symmetry-related benzene rings (Fig. 2).

Refinement
Allylic CH group was found to be disordered over two sites, C21 and C22, and occupancies were refined with the sum constrained to unity. In order to get a sensible geometry for the minor part, bond length C3-C22 was restrained to 1.480 (15)Å.
C-bonded H atoms were placed in idealized positions and refined as riding to their carrier C atoms, with bond lengths fixed to 0.93Å (aromatic and allylic H atoms) or 0.97Å (methylene CH 2 ). Hydroxyl H atom H14 was found in a difference map and refined as riding to O14, with the O-H bond length fixed to the found value, 0.883Å. Isotropic displacement parameters supplementary materials sup-2 for H atoms were calculated as U iso (H) = 1.2U eq (carrier atom) for C-bonded H atoms and U iso (H) = 1.5U eq (O14) for H14.
Measured Friedel pairs were merged in the final refinement. Fig. 1. The structure of the title compound with displacement ellipsoids at the 30% probability level. C22 (minor part of the disorder) has been omitted for clarity. The inset shows the complete structure. Colour code: green for C21-disordered part; purple for the C22-disordered part. Fig. 2. A part of the crystal structure of the title compound, including hydrogen bonds depicted with blue dashed lines, and C-H···π contacts from the asymmetric unit, represented as red dashed lines. Colour code for symmetry-related molecules: blue -x, -1/2+y, -z; green -x, 1/ 2+y, -z; red 1-x, 1/2+y, -z; gold x, 1+y, z.