DFT study of the geometries and vibrational spectra of indene and some of its heterocyclic analogues, benzofuran, benzoxazole, bensothiophene, benzothiazole, indole and indazole

Ab-initio optimized geometries and harmonic force fields were calculated for indene, 1; benzofuran, 2; benzoxazole, 3; benzothiophene, 4; benzothiazole, 5; indole, 6; and indazole, 7, at the HF and B3LYP levels of theory using the 6-31G** basis set. A planar Cs symmetry was assumed in all calculations. The force fields of 1-6 were scaled with respect to the experimental frequencies available in literature. The calculated frequencies confirmed the experimental assignment of these molecules, 1-6. The calculated scale factors were used to calculate vibrational frequencies of 7 and showed possible misassignments in the experimental vibrational frequencies of 7.