An investigation into the substituent effect of halogen atoms on the crystal structures of indole-3-carboxylic acid (ICA) was written by Luo, Yang-Hui;Sun, Bai-Wang. And the article was included in CrystEngComm in 2013.Electric Literature of C9H6ClNO This article mentions the following:
A study into the substituent effect of halogen atoms (F, Cl, Br) on the crystal structure of indole-3-carboxylic acid (ICA) was prepared The study was done through the aspect of crystal structure, intermol. interactions and π···π stacking motifs with the assistance of IR spectra, elemental analyses, NMR spectra, DSC, thermogravimetric analyses (TGA) and hot stage microscopy (HSM) measurements. The different kinds of halogen atoms and the different substituted positions have a significant effect on the crystal structures, mol. π···π stacking motifs and the kinds of intermol. interactions. The authors further correlated the m.ps. of the ICAs with the H-H, O-H and X-H (X = F, Cl, Br) interactions, and found a pos. correlation between them. In the experiment, the researchers used many compounds, for example, 5-Chloroindole-3-carboxaldehyde (cas: 827-01-0Electric Literature of C9H6ClNO).
5-Chloroindole-3-carboxaldehyde (cas: 827-01-0) belongs to indole derivatives. Indole, also called Benzopyrrole, a heterocyclic organic compound occurring in some flower oils, such as jasmine and orange blossom, in coal tar, and in fecal matter. Due to this activity, the indole ring system has become an important component or intermediate in the synthesis of heterocycles.Electric Literature of C9H6ClNO
Referemce:
Indole alkaloid derivatives as building blocks of natural products from Bacillus thuringiensis and Bacillus velezensis and their antibacterial and antifungal activity study,
Preparation of Indole Containing Building Blocks for the Regiospecific Construction of Indole Appended Pyrazoles and Pyrroles