The compound 5-tert-Butyl-8-methyl-2,3-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-1-one, (3) was synthesized and characterized by H-1 NMR, IR, and mass spectroscopy. Its molecular structure was solved by single crystal X-ray diffraction method. The crystal structure analysis revealed that two different conformers of compound 3 are present in the crystal. The difference in two conformational structures was found in the arrangement of CO group to the plane of the molecule. The hydrogen bonding of the two conformers was not similar. The Hirshfeld surface analyses and two-dimensional finger plots showed that the two conformers are completely different. [Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file: Spectral data (MS, NMR, PXRD, DSC, and TGA) of the compound 3 are available in the supporting information in .pdf format. Crystallographic information file (.cif) of compound 3 is available in the electronic format.]