3-(4-Chlorophenyl)-2-methylacrylic acid

In the crystal structure of the title compound, C10H9ClO2, dimers form as a result of intermolecular O—H⋯O bonding. These dimers are linked to each other via C—H⋯O bonds, where the CH group belongs to the benzene ring and the O atom is from the carbonyl group of an adjacent molecule. There exist two intermolecular C—H⋯O hydrogen bonds, which individually form five-membered rings. There also exists a π–π interaction between the aromatic ring and its symmetry counterpart, with a centroid–centroid distance of 4.0202 (17) Å, and a C—H⋯π interaction between a methyl CH group and the aromatic ring.

In the crystal structure of the title compound, C 10 H 9 ClO 2 , dimers form as a result of intermolecular O-HÁ Á ÁO bonding. These dimers are linked to each other via C-HÁ Á ÁO bonds, where the CH group belongs to the benzene ring and the O atom is from the carbonyl group of an adjacent molecule. There exist two intermolecular C-HÁ Á ÁO hydrogen bonds, which individually form five-membered rings. There also exists ainteraction between the aromatic ring and its symmetry counterpart, with a centroid-centroid distance of 4.0202 (17) Å , and a C-HÁ Á Á interaction between a methyl CH group and the aromatic ring.

Comment
Cinnamic acids compose a relatively large family of organic acid isomers (Bravo, 1998). In nature, cinnamic acid derivatives are important metabolic building blocks in the production of lignins for higher plants. Cinnamic acid possesses antibacterial, antifungal and parasite fighting abilities (Burt, 2004). A derivative of cinnamic acid is an important pharmaceutical for high blood pressure, stroke prevention and possess antitumour activity (Hertog et al., 1995). In continuation of our efforts to synthesize various derivatives of cinnamic acids (Niaz et al., 2008, Muhammad, Ali et al., 2008 and their tin complexes (Muhammad et al., 2008a(Muhammad et al., , 2008b, we herein report the structure of the title compound (I).
In the crystal structure of the title compound, the C-C bonds are in the range [1.467 (3) and Cg iii [Cg is the center of the (C5-C10) benzene ring]. There also exist a π···π-interaction between the benzene rings of adjacent molecules. The distance between the centroids of Cg and Cg iv [symmetry code: iv = -x + 1, -y + 1, -z + 1], is 4.0202 (17) Å.

Experimental
Compound (I) was prepared according to the reported procedure (Muhammad et al., 2007a). A mixture of 4-chlorobenzaldehyde (1.40 g, 10 mmol), methylmalonic acid (2.36 g, 20 mmol) and piperidine (1.98 ml, 20 mmol) in a pyridine (12.5 ml) solution was heated on a steam-bath for 24 h. The reaction mixture was cooled and added to a mixture of 25 ml of concentrated HCl and 50 g of ice. The precipitate formed in the acidified mixture was filtered off and washed with ice-cold water. The product was recrystallized from ethanol. The yield was 89%.

Refinement
The coordinates of H atom attached to O1 were refined freely. All other H atoms were positioned geometrically, C-H = 0.93, and 0.96 Å for aromatic and methyl H, and constrained to ride on their parent atoms and were treated as isotropic with U iso (H) = xU eq (C,O), where x = 1.5 for methyl H, and x = 1.2 for all other H atoms. Fig. 1. ORTEP drawing of (I) with the atom numbering scheme. The thermal ellipsoids are drawn at the 50% probability level. The intramolecular H-bonds are shown by doted lines.

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 Rfactors(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.