Tautomerism aspect of thione-thiol combined with spectral investigation of some 4-amino-5-methyl-1,2,4-triazole-3-thione Schiff's bases

• Published in: Journal of molecular structure 2017-10, Vol.1146, p.432-440
• Main Authors: El Ashry, El Sayed H., Awad, Laila F., Soliman, Saied M., Abd Al Moaty, Mohamed N., Ghabbour, Hazem A., Barakat, Assem
• Format: Article
• Language: English
• Subjects: 1,2,4-Triazole; DFT calculations; NMR; Schiff's bases; Tautomerism; Thione
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2017.06.002

Reaction of 4-amino-3-methyl-1,2,4-triazole-5-thione with some substituted benzaldehydes in presence of catalytic amount of hydrochloric acid afforded the respective Schiff's bases 3a-e. Computational studies using DFT incorporating the B3LYP/6-311G(d,p) level of theory is used to predict the stability of the possible tautomers. Molecular modeling, natural charge calculations, NMR, Frontier molecular orbitals and electronic spectra were investigated. Analysis of the thermodynamic parameters of the thione-thiol tautomeric reactions of these derivatives was used to predict the tautomers stability. The thione tautomer is the most favored form in gas phase and in solution whatever the nature of solvent used. The electronic spectra were assigned based on the TD-DFT calculations. The GIAO NMR chemical shifts correlated well with the experimental data. Optimized molecular structure and the HOMO-LUMO plot calculated by the hybrid B3LYP/6-311G++(d,p) method for 4-(4-Chlorobenzylidene)amino-5-methyl-1,2,4-triazole-3-thione 3a. [Display omitted] •Stability calculations of some substituted 1,2,4-triazole-3-thione tautomers.•Study frontier molecular orbitals calculations for the studied compounds.•NMR study for the substituted 1,2,4-triazole-3-thione Schiff's bases.