(RS)-Benzyl mandelate

# 2004 International Union of Crystallography Printed in Great Britain ± all rights reserved A benzyl ester of mandelic acid, C15H14O3, was obtained by the crystallization of racemic mandelic acid from benzyl alcohol followed by vacuum drying at 363 K. The structure is composed of two hydrogen-bonded chains of S or R con®guration, running along the shortest crystallographic b axis. There is one molecule in the asymmetric unit and each molecule forms four intermolecular hydrogen bonds with two other molecules of the same chirality.

A benzyl ester of mandelic acid, C 15 H 14 O 3 , was obtained by the crystallization of racemic mandelic acid from benzyl alcohol followed by vacuum drying at 363 K. The structure is composed of two hydrogen-bonded chains of S or R con®guration, running along the shortest crystallographic b axis. There is one molecule in the asymmetric unit and each molecule forms four intermolecular hydrogen bonds with two other molecules of the same chirality.

Comment
During the crystallization of racemic mandelic acid from benzyl alcohol and drying off the solvent in a vacuum oven, colourless needle-shaped crystals of (RS)-benzyl mandelate (BM), (I), were obtained. The crystal structure of this compound was not found in the Cambridge Structural Database (CSD, Version 1.6; Allen, 2002) and hence its structure was determined by single-crystal X-ray diffraction at 150 K.
The compound BM has one molecule in the asymmetric unit. Fig. 1 shows the structure and the atom labelling. The bond lengths and angles are unexceptional. Each molecule forms four intermolecular hydrogen bonds to two neighbouring molecules, as shown in Fig. 2. The unit-cell contents of BM are shown in Fig. 3.
The crystal structure is composed of two types of chains that run along the shortest crystallographic axis, b, which is the needle axis. The C 1 1 (5) chain runs through the hydroxyl and carbonyl groups via ÐC OÁ Á ÁHÐOÐ hydrogen bonding.
The C 1 1 (2) chain arises from the linking of OH in one molecule to OH of another molecule. Fig. 4 shows the packing of the two chains and the resulting bilayer sandwich. Layers of hydrogen-bonded chains are sandwiched between bilayers of phenyl rings. There is face±edge interaction between the phenyl rings of each molecule, and also between the phenyl rings of adjacent molecules in the same chain. Each C 1 1 (5) and C 1 1 (2) chain is composed of either all-S con®guration molecules or all-R molecules, and the chains pack such that there are alternating R and S chains, as shown in Fig. 5. There are no hydrogen-bonding interactions between R and S molecules. The hydrogen bonds are listed in Table 1.

Experimental
A saturated solution of racemic mandelic acid (supplied by SigmaÐ Aldrich, 99%) in benzyl alcohol was prepared at 323 K and stirred at 343 K for 2 h. On cooling to 298±303 K, needle-shaped crystals of racemic mandelic acid formed; these were vacuum-®ltered and then dried in a vacuum oven at 363 K to remove benzyl alcohol mother liquor. After a few weeks in the vacuum oven, crystals of (RS)-benzyl mandelate were found alongside an orange±yellow amorphous glasslike residue.  Hydrogen bonds (dashed lines) formed by each independent molecule with the neighbouring two molecules.

Figure 3
The unit-cell contents of BM, viewed along b.
All H atoms were located in a difference Fourier map and re®ned isotropically.
Data collection: COLLECT (Nonius, 1997±2000); cell re®nement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL SCALEPACK and DENZO (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999). 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.