Density functional theory treatment of the structures and vibrational frequencies of 2,4- and 2,6-dinitrotoluenes

The subject of study in this investigation were the dinitrotoluenes (DNT), 2,4-DNT, and 2,6-DNT. Molecular orbital calculations at the Density Functional Theory (B3LYP) level with the 3-21G, 6-31G, 6-31G(d), 6-311G, 6-311G(d), and 6-311+G(d,p) family of basis sets from the Gaussian system of programs were used. The most stable conformers, their structural parameters, IR vibrational frequencies and intensities, were determined. This information gives the vibrational spectroscopic signatures of the two DNT isomers. The largest basis set yielded the lowest energy conformation. The best results, in terms of reproducing experimental data, were obtained with the 6-311+G** basis set for booth isomers. A comparison between the 2,4 and 2,6-DNT spectra show that the 2,6-DNT spectrum presents less vibrational bands due to higher symmetry.