Fourier transform infrared and Raman spectra, vibrational assignment and ab initio calculations of terephthalic acid and related compounds

The Fourier transform infrared and Raman spectra of solid terephthalic acid, p-C6H4(COOH)2, have been recorded, and the Fourier transform Raman spectra for the terephthalate anion were measured. The wavenumbers for the band positions have been calculated in order to assign them. Moller–Plesset (MP2) and Density functional theory (DFT) calculations have been carried out with Huzinaga–Dunning basis sets (DZV). Also, a normal coordinate analysis through the Wilson–El'yashevich method was performed. The differences between the calculated ab initio spectra and the spectra of the solid phase have been interpreted with respect to the different C2h and Ci local symmetry in the gas and in the solid phase, respectively, and considering also the formation of long-chains of terephthalic acid in the solid phase. In spite to the absence of experimental data for the cis conformation, calculations have been carried out and structural parameters and infrared intensities have been evaluated for the trans and cis conformations of terephthalic acid.