Ibuprofen-thiadiazole hybrid compounds: Synthesis, vibrational analysis and molecular structure of 5-(1-(4-isobutylphenyl)ethyl)-1,3,4-thiadiazol-2-amine hydrochloride

Abstract

The ibuprofen derivative 5-(1-(4-isobutylphenyl)ethyl)-1,3,4-thiadiazol-2-amine hydrochloride is prepared by via cyclization of ibuprofen with thiosemicarbazide in the presence of POCl3. The compound has been characterized by using FT-IR and multinuclear (1H and 13C) NMR spectroscopies, and elemental analysis. The molecular structure in crystalline phase has been determined by single crystal X-Ray diffraction. The compound crystallizes in the triclinic system with space group P-1 as discrete cations and chloride anions with two enantiomers present in the asymmetric unit. A full vibrational analysis of the FT-IR and FT-Raman spectra has been performed in conjunction with quantum chemical calculations. Experimental data agree with the occurrence of the thiadiazole NH protonated form in the solid phase. The observation of the ν(NN) and δ(CNN) normal modes as strong signals in the infrared and Raman spectra at 1189 (1180 cm−1) and 774 cm−1 suggests a NN bond with partial double bond character in the thiadiazole moiety, in good agreement with the computed values at the B3LYP/6-311++G(d,p) level of approximation. The NBO analysis showed that both, the sulfur lone pair and the exocyclic amine nitrogen lone pair orbitals contribute to strong resonance interactions with the adjacent π*(N2=C8) antibonding orbital of the protonated thiadiazole group.