Quantum chemical determination of molecular geometries and interpretation of FT-IR and FT-Raman spectra for 3,4-dinitrotoluene

Abstract

The FT-IR and FT-Raman vibrational spectra of 3,4-dinitrotoluene (3,4-DNT) have been recorded in the region 400-4000 cm^{<span style="font-family:Symbol;mso-ascii-font-family: " times="" new="" roman";mso-hansi-font-family:"times="" roman";mso-char-type:symbol;="" mso-symbol-font-family:symbol"="" lang="EN-GB">-1</span>} and 50-3500 cm^{<span style="font-family:Symbol;mso-ascii-font-family: " times="" new="" roman";mso-hansi-font-family:"times="" roman";mso-char-type:symbol;="" mso-symbol-font-family:symbol"="" lang="EN-GB">-1</span>}, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on DFT (Density Functional Theory)-B3LYP using 6-31+G(d,p) and6-311++G(d,p) basis sets. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been compared with experimental FT-IR and FT-Raman spectra. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) energies confirms the occurrence of ICT (Intramolecular Charge Transfer) within the molecule. The calculated HOMO and LUMO energy gaps also confirm that charge transfer occurs within the molecule. A sufficient general agreement between the theoretical and the experimental spectra has been achieved.