9-Ethyl-9H-carbazole-3-carbaldehyde

The title molecule, C15H13NO, approximates a planar conformation except for the alkyl chain (ethyl group) bonded to the N atom with a maximum deviation from the least-squares plane through the 15 planar atoms of 0.120 (2) Å for the O atom. The distance of the formyl O atom from the plane of the carbazole ring is 0.227 (2) Å. The N—C bond lengths in the central ring are significantly different, reflecting the electron-withdrawing properties of the aldehyde group. As a consequence, charge transfer may occur from the carbazole N atom to the substituted benzene ring.

The title molecule, C 15 H 13 NO, approximates a planar conformation except for the alkyl chain (ethyl group) bonded to the N atom with a maximum deviation from the leastsquares plane through the 15 planar atoms of 0.120 (2) Å for the O atom. The distance of the formyl O atom from the plane of the carbazole ring is 0.227 (2) Å . The N-C bond lengths in the central ring are significantly different, reflecting the electron-withdrawing properties of the aldehyde group. As a consequence, charge transfer may occur from the carbazole N atom to the substituted benzene ring.

Related literature
For the properties of carbazole derivatives, see: van Dijken et al. (2004); Li et al. (2005). For the X-ray structure of 9-ethyl-3,6-diformyl-9H-carbazole, see: Wang et al. (2008) and of 9ethyl-9H-carbazole, see: Kimura et al. (1985). between the oxygen atom O1 and the plane of the carbazole ring. And the distance from the oxygen atom O1 to the carbazole plane (the least-squares plane defined by all the 13 atoms of the carbazole framework) is 0.227 (2) Å. The remarkable difference of N-C bond lengths is observed in this structure: N1-C1 = 1.372 (3), N1-C12 = 1.391 (3) Å, which is obviously different from that of 9-ethyl-3,6-diformyl-9H-carbazole (Wang et al., 2008) and that of 9-ethyl-9H-carbazole (Kimura et al., 1985). The different N-C bond lengths maybe root from the structural asymmetry. The pull-electron property of aldehyde group induces a charge-transfer from nitrogen atom N1 to the benzene ring which connects with the aldehyde group.
Experimental 9-Ethyl-9H-carbazole (0.30 g, 1.54 mmol) was dissolved in N,N-dimethylformamide (DMF, 10 ml). After cooling the mixture to 273 K, a DMF solution of POCl 3 (0.24 g, 1.60 mmol) was slowly added. After stirring for 10 h., the mixture was poured into ice water and further stirred for 0.5 h. The solution was extracted with chloroform and dried over Na 2 SO 4 .
After removing the solvent, the crude product was purified by recrystallization from ethanol, affording the title compound, (I) (0.29 g, 85%). Then, compound (I) was dissolved in a mixture of solvents, chloroform and hexane, and colorless block crystals were formed on slow evaporation at room temperature over one week.

Refinement
All H atoms were placed in geometrically calculated positions and refined using a riding model with C-H = 0.93 Å (for aromatic CH), C-H = 0.97 %A (for CH 2 groups), and 0.96 %A (for CH 3 groups). Their isotropic displacement parameters were set to 1.2 times (1.5 times for CH 3 groups) the equivalent displacement parameter of their parent atoms.  Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 30% probability level.