Vibrational, electronic and quantum chemical studies of 1,2,4-benzenetricarboxylic-1,2-anhydride

The FTIR and FT-Raman spectra of 1,2,4-benzenetricarboxylic-1,2-anhydride (BTCA) have been recorded in the range 4000–400 and 4000–100 cm−1, respectively. The complete vibrational assignments and analysis of BTCA have been performed. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP, MP2, B3PW91) method using 6-311++G**, 6-31G** and cc-pVTZ basis sets. The structural parameters, energies, thermodynamic parameters, vibrational frequencies and the NBO charges of BTCA were determined by the DFT method. The 1H and 13C isotropic chemical shifts (δ ppm) of BTCA with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. The delocalization energies of different types of interactions were determined.

The FT-IR, FT-Raman, 1H and 13C NMR spectral measurements of 1,2,4-benzenetricarboxylic-1,2-anhydride and complete assignments have been discussed. The optimised geometry with 6-31G(d,p), 6-311++G(d,p) and cc-pVTZ basis sets were used to determine energy, structural parameters, vibrational frequencies, IR and Raman intensities. The influence of various factors regarding the stability, electronic interactions and the chemical shifts have been discussed. A detailed natural bond orbital analysis was carried out to ascertain the charge distribution.Figure optionsDownload as PowerPoint slideHighlights
► Vibrational and NMR studies of 1,2,4-benzenetricarboxylic-1,2-anhydride are reported.
► The bond angle is greater than 120° where the COOH group is attached.
► The chemical shift of carbonyl carbon atoms are lies in the downfield.
► The ELUMO–EHOMO is 5.10 eV while the chemical hardness is 2.55 eV.
► The electrostatic potential limits are +9.365e × 10−2 and −9.365e × 10−2.