Crystal structure of 3-ethynylbenzoic acid

In the title compound, C9H6O2, the carboxylic acid group is almost in the plane of the benzene ring, making a dihedral angle of 2.49 (18)°. In the crystal, molecules are linked by pairs of O—H⋯O hydrogen bonds, forming classical acid–acid inversion dimers, with an R 2 2(8) ring motif. The dimers are linked by pairs of C—H⋯O hydrogen bonds forming chains, enclosing R 2 2(16) ring motifs, propagating along the c-axis direction.

In the title compound, C 9 H 6 O 2 , the carboxylic acid group is almost in the plane of the benzene ring, making a dihedral angle of 2.49 (18) . In the crystal, molecules are linked by pairs of O-HÁ Á ÁO hydrogen bonds, forming classical acid-acid inversion dimers, with an R 2 2 (8) ring motif. The dimers are linked by pairs of C-HÁ Á ÁO hydrogen bonds forming chains, enclosing R 2 2 (16) ring motifs, propagating along the c-axis direction.

Related literature
For the potential applications of terminal alkynes in crystal engineering, see: Dai et al. (2004). For the synthesis of the title compound, see: Bischoff et al. (2008). For the NMR spectrum of the title compound, see: Bleisch et al. (2014). For other syntheses of the title compound, see: Jones et al. (2008);Pawle et al. (2011). For the crystal structure of the 4-ethynyl benzoic acid methyl ester, see: Dai et al. (2004 Table 1 Hydrogen-bond geometry (Å , ).

Crystal structure of 3-ethynylbenzoic acid
Chiara Venturini, Nicolas Ratel-Ramond and Andre Gourdon S1. Chemical context In recent years, the interest in compounds with an alkyne C≡CH bond has increased due to their versatility in coupling reactions such as Glaser-Hay or Sonogashira. At the same time the crystallography of terminal alkynes has become an intense field of study for the potential applications in crystal engineering (Dai et al., 2004). Additionally, the presence of a carboxylate group on these compounds makes them potential candidates for the formation of metal organic frameworks viz. MOFs. With these applications in mind, we have synthesized the title compound and report herein on its crystal structure.The synthesis of 4-ethynylbenzoic acid has been reported previously (Jones et al., 2008;Pawle et al., 2011), but not its crystal structure. Only the crystal structure of the ester, 4-ethynylmethylbenzoate, has been described previously (Dai et al., 2004).

S2. Synthesis and crystallization
3-ethynylbenzoic acid is commercially available. In this work it was obtained by saponification and acidification of the corresponding ester in methanol/water with lithium hydroxide, following the reported procedure (Bischoff et al., 2008).

S2.1. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All of the H atoms were located in difference Fourier maps and freely refined.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view along the a axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1).  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.13 e Å −3 Δρ min = −0.13 e Å −3 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 esds are taken into account in the estimation of distances, angles and torsion angles