The structures of 2-(3-hydroxy-5-methylphenoxy)-N-(4-nitrophenyl)acetamide), B1, and 2-(3-hydroxy-5-methylphenoxy)-N-(4-(trifluoromethyl)phenyl)acetamide, B2, are crystallized in the crystal symmetry of the monoclinic structure and in the space group of P21/c. For the different structures of B1 and B2, B1 displays an absolute planarity conformation with torsion angles of 172.2–179.1. The two molecules of B1 are linked by a hydrogen bond of N–H…O–N–O, where a hydrogen atom of amide is bound to an oxygen atom of the nitro-substituted group. In the case of B2, the molecules are connected to each other through the hydrogen bonding interaction of C=O…H–O. DFT calculations reveal that the transition from HOMO to LUMO of B1 and B2 shows the absorption bands B1 and B2 at 314 and 240 nm, respectively. Upon the addition of an OH− ion, the absorption bands of B1 and B2 shift to a longer wavelength than the original bands of B1 and B2. According to the 1H-NMR results, the NH proton of B1 and B2 disappears due to the deprotonation process. The methylene group and aromatic region move to upfield shift when adding an OH− ion.