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

摘要

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 POC13. The compound has been characterized by using FT-IR and multinuclear (H-1 and C-13) 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 N-H protonated form in the solid phase. The observation of the v(N=N) and delta(CNN) normal modes as strong signals in the infrared and Raman spectra at 1189 (1180 cm(-1)) and 774 cm(-1) suggests a N=N 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 pi*(N2=C8) antibonding orbital of the protonated thiadiazole group. (C) 2018 Elsevier B.V. All rights reserved.