Theoretical DFT and experimental Raman and NMR studies on thiophene, 3-methylthiophene and selenophene

The results of extended MO calculations using density functional theory (DFF) approximation supported by experimental Raman, H-1 and C-13 NMR studies on thiophene are reported. Raman spectra of liquid thiophene were re-examined and the performance of a hybrid B3PW91 density functional was compared with the ab initio restricted Hartree-Fock (RHF) method. With the basis sets of the 6-311++G** quality, the DFF calculated bond lengths, dipole moments and harmonic vibrations were predicted in a very good agreement with available experimental data. Additionally, the results on thiophene were extended by calculations on 3-methylthiophene and selenophene. In this case, a significant change in geometry and charge distribution in thiophene ring due to a methyl group substituent or replacement of sulphur by selene atom was observed. A linear correlation between the predicted harmonic vibrational frequencies (scaled using SQM method) and experimental ones for thiophene, selenophene and 3-methylthiophene was shown. The theoretically calculated spectra have satisfactorily reproduced the available experimental spectra for thiophene and selenophene. (C) 2002 Elsevier Science B.V. All rights reserved.