Synthesis, X-ray, NMR, FT-IR, UV/vis, DFT and TD-DFT studies of N-(4-chlorobutanoyl)-N′-(2-, 3- and 4-methylphenyl)thiourea derivatives

• Synthesis of a three new thiourea isomers.
• Chemical structures were characterized using X-ray and spectroscopic techniques.
• DFT and TD-DFT were used to investigate the isomerization effect on spectra data.
• The isomerization has an important influence on UV/vis absorption bands.
• The isomerization effect on vibration modes and chemical shifts is negligible.

A new isomers of thiourea derivatives, namely N-(4-chlorobutanoyl)-N′-(2-methylphenyl)-thiourea (1a), N-(4-chlorobutanoyl)-N′-(3-methylphenyl)thiourea (1b) and N-(4-chlorobutanoyl)-N′-(4-methylphenyl)thiourea (1c) have been synthesized by refluxing mixture of equimolar amounts of 4-chlorobutanoylisothiocyanate with 2, 3 or 4-toluidine, respectively. The three isomers were characterized by spectroscopic (UV/vis, FT-IR and NMR) and X-ray crystallography techniques. To investigate the isomerization effect on spectroscopic data, DFT and TD-DFT calculations have been carried out using five hybrid functionals (B3LYP, B3P86, CAM-B3LYP, M06-2X and PBE0) to predict UV/vis absorption bands (n → π∗ and π → π∗), 1H and 13C NMR chemical shifts, FT-IR vibration modes and X-ray parameters (bonds, bond angles and torsion angles) for 1a, 1b and 1c isomers. The results showed that the isomerization effect is significant on λMAX absorption bands, while for IR and NMR the effect is negligible. In accordance with previous studies, B3LYP, B3P86 and PBE0 gave the most reliable to predict the excitation energies of thiourea derivatives.

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