4-(2-Benzoyl­ethyl)benzoic acid

Roger A Lalancette; Hugh W Thompson

doi:10.1107/S1600536808019387

. 2008 Jul 5;64(Pt 8):o1399. doi: 10.1107/S1600536808019387

4-(2-Benzoylethyl)benzoic acid

Roger A Lalancette ^a,^*, Hugh W Thompson ^a

PMCID: PMC2962032 PMID: 21203119

Abstract

The title compound, C₁₆H₁₄O₃, adopts a conformation in which each functional group is almost coplanar with its adjacent ring, while the two aromatic rings are twisted with respect to one another with a dihedral angle of 78.51 (3)°. The compound dimerizes by standard centrosymmetric hydrogen-bonded carboxyl pairing [O⋯O = 2.6218 (11) Å and O—H⋯O = 176 (2)°]. The packing includes two intermolecular C—H⋯O close contacts with the ketone group.

Related literature

For related literature, see: Borthwick (1980 ▶); Steiner (1997 ▶).

Experimental

Crystal data

C₁₆H₁₄O₃
M _r = 254.27
Monoclinic,
a = 7.3066 (1) Å
b = 8.7363 (1) Å
c = 19.6707 (3) Å
β = 90.296 (1)°
V = 1255.62 (3) Å³
Z = 4
Cu Kα radiation
μ = 0.75 mm⁻¹
T = 100 (2) K
0.27 × 0.21 × 0.15 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2001 ▶) T _min = 0.871, T _max = 0.926
8836 measured reflections
2250 independent reflections
2122 reflections with I > 2σ(I)
R _int = 0.024

Refinement

R[F ² > 2σ(F ²)] = 0.032
wR(F ²) = 0.085
S = 1.06
2250 reflections
177 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.15 e Å⁻³

Data collection: APEX2 (Bruker, 2006 ▶); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005 ▶); program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808019387/fl2203sup1.cif

e-64-o1399-sup1.cif^{(17.4KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808019387/fl2203Isup2.hkl

e-64-o1399-Isup2.hkl^{(110.6KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3A⋯O2ⁱ	0.97 (2)	1.66 (2)	2.6218 (11)	176 (2)
C5—H5⋯O1ⁱⁱ	0.95	2.59	3.3786 (14)	140
C8—H8A⋯O1ⁱⁱⁱ	0.99	2.54	3.4864 (14)	160

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

HWT is grateful to Professor Gree Loober Spoog for helpful consultations. The authors acknowledge support by NSF–CRIF grant No. 0443538.

supplementary crystallographic information

Comment

Our X-ray study of ketocarboxylic acids seeks to uncover the structural features governing the choice among the five known keto–acid hydrogen-bonding modes. One major determinant is the availability of centrosymmetry, such that carboxyl dimerization, overall the commonest type of aggregation, is rare among single enantiomers. A second important influence is molecular flexibility, as reflected by the number of fully rotatable bonds in the molecule, with dimerization becoming less common as structural or conformational rigidity increases. In this context, the title molecule (I) is relatively flexible, containing four fully rotatable bonds in addition to the carboxyl.

Fig. 1 shows the asymmetric unit for (I) with its numbering. A principal feature is the near coplanarity of the two carbonyl-bearing functional groups with their respective benzene rings, permitting strong conjugation. The phenone's dihedral angle is 7.83 (8)° (C8—C9—C10—O1 versus C10—C11—C12—C13—C14—C15) and that for the carboxylic acid is 19.92 (6)° (C1—C16—O2—O3 versus C1—C2—C3—C4—C5—C6). The connecting alkyl chain, however, is not maximally staggered, the C4—C7—C8—C9 torsion being -160.20 (10)° rather than 180°. The two separate aromatic rings lie at a mutual dihedral angle of 78.51 (3)°.

Carboxyl dimers often display complete or partial averaging of C—O bond lengths and C—C—O angles due to disorder; however, no significant averaging is observed in (I), where these lengths and angles are similar to those in other highly ordered carboxyl situations (Borthwick, 1980).

Fig. 2 shows the packing arrangement for (I), typical for acids that are either racemic or, as with (I), achiral but capable of forming conformational racemates. Centrosymmetric dimers with two different orientations are centered at 1/2,1/2,1/2 and 1/2,0,0 in the chosen cell. The eight-membered carboxyl dimer of one orientational type lies close to the phenone aromatic ring in a dimer of the second type and nearly parallel to it [dihedral angle = 6.38 (7)°]. The normal distance from the centroid of this ring to the carboxyl-dimer plane = 3.472 Å and the intermolecular acid-to-ketone O═C···C═O distance = 3.3508 (15) Å.

Two intermolecular C—H···O═C close contacts were found in the packing, linking the ketone (O1) to H8A and to H5 in separate neighboring molecules (Table 1). These contacts lie within the 2.6 Å range we routinely survey for non-bonded dipolar packing interactions (Steiner, 1997).

Experimental

Methyl 4-(3-oxo-3-phenyl-1-propenyl)benzoate, purchased from Acros Organics/Fisher Scientific, Springfield, NJ, USA, was hydrogenated in ethyl acetate at atmospheric pressure and room temperature over a 5% Pd/C catalyst. The resulting reduced methyl ester, m.p. ca 365 K, was saponified by refluxing with aqueous KOH to yield (I). Crystals of X-ray quality were obtained from Et₂O, m.p. 431 K. Typically for carboxyl-paired keto acids, the solid-state (KBr) and the solution infrared spectra of (I) display only slight differences in the C═O region. The former features intense absorption at 1682 cm^-1 for both C═O functions; in CHCl₃ solution this combined peak is seen at 1688 cm^-1.