1-Vinyl-1H-indole-3-carbaldehyde

In the title compound, C11H9NO, the C and O atoms of the attached carbaldehyde group deviate by just 0.052 (2) and 0.076 (1) Å, respectively, from the mean plane of the indole ring system. In addition to van der Waals forces, the molecular packing is stabilized by C—H⋯O hydrogen bonds, which form a C(7) chain motif, and π–π interactions (centroid–centroid distance 3.637 Å) between the pyrrole and benzene rings of the indole ring system.

In the title compound, C 11 H 9 NO, the C and O atoms of the attached carbaldehyde group deviate by just 0.052 (2) and 0.076 (1) Å , respectively, from the mean plane of the indole ring system. In addition to van der Waals forces, the molecular packing is stabilized by C-HÁ Á ÁO hydrogen bonds, which form a C(7) chain motif, andinteractions (centroidcentroid distance 3.637 Å ) between the pyrrole and benzene rings of the indole ring system.

Comment
Indoles and their derivatives have been interest for many years, since large number of natural products contain indole systems and they are found in a number of pharmaceutical products, fragrances and dyes (Padwa et al., 1999). Indole derivatives are identified as interfering with a G protein-independent signaling pathway of the CRTH2 receptor (Mathiesen et al., 2005). These derivatives possess antidepressant (Grinev et al., 1984), anti-microbial (Gadaginamath & Patil, 1999) and anti-inflammatory (Rodriguez et al., 1985) activities. In view of its importance, we have undertaken the single-crystal X-ray diffraction study and report here its results.
The X-ray study confirmed the molecular structure and atomic connectivity for (I), as illustrated in Fig. 1. The geometry of the indole ring system is comparable to those reported for other indole derivatives (Karthick et al., 2005;Selvanayagam et al., 2005;Sonar et al., 2005). The bond length of C9-C10 [1.284 (2) Å] confirms the double bond character (Allen et al., 1987). The sum of the angles at N1 of the indole ring (360°) is in accordance with sp 2 hybridization.
The indole ring is planar with a maximum deviation of 0.017 (1) Å for atom C8. The carbaldehyde group atoms C11 and O1 deviate 0.052 (2) and 0.076 (1) Å, respectively from the best plane of the indole ring.
In addition to the van der Waals forces, the molecular packing is stabilized by intermolecular C-H···O hydrogen bond (Table 2). Atom H9 of C9 forms a intermolecular hydrogen bond with oxygen atom O1 forming a C(7) chain motif of C-H···O hydrogen bond along the diagonal of ac plane (Fig. 2). In addition to this a weak π···π interaction between the pyrrole ring (N1/C1/C6-C8) at (x,y,z) and benzene ring (C1-C6) at (1 -x, -y), -z) stabilizes the molecular packing. The centroid-to-centroid distance is 3.637Å.

Experimental
A mixture of N-vinylindole (0.05 mol) and DMF (0.15 mol) was stirred with POCl 3 (32.3 ml). The reaction mixture was poured into ice water (300 ml) and stirred for 30minutes at less than 10° C. The precipitated solid was collected by filtration and washed well water (100 ml). In order to get the diffraction quality crystals, the compound was recrystallized from ethyl acetate.

Refinement
The H atoms were positioned geometrically with C-H distances of 0.93 Å and were included in the refinement in the riding motion approximation with U iso = 1.2U eq (C).
supplementary materials sup-2 Figures   Fig. 1. The structure and atom-numbering scheme for the title compound; displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radius.  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.81283 (15