Molecular structure and infrared spectra of furan, thiophene, selenophene and their 2,5-N and 3,4-N derivatives: density functional theory and conventional post-Hartree-Fock MP2 studies

Molecular parameters (bond lengths and bond angles, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of furan, thiophene, selenophene and their 2,5-N and 3,4-N derivatives have been predicted by density functional theory with the combined Becke3-LYP gradient exchange-corrected functional (DFT(B3LYP)) and the conventional ab initio MP2(full) approach. The standard 6-31G(d,p) basis set was used for all atoms except selenium for which a partially uncontracted Huzinaga basis set supplemented with a set of d-polarization functions was employed. Results are compared with the available experimental data. The molecular parameters computed by means of the DFT method are in a good agreement with those predicted by the MP2 approach and with the experimental data. The calculated data suggest verification of the experimental data for the bond angles of selenophene. Very good agreement between the calculated IR wavenumbers and absorption IR intensities of the molecules studied and their deuterated species by the DFT method and the experimental data was found. (C) 1997 Elsevier Science B.V.