Evaluation of the structural properties of powerful pesticide dieldrin in different media and their complete vibrational assignment

Abstract

Dieldrin was characterized by using Fourier Transform infrared (FT-IR) and Raman (FT-Raman), UltravioleteVisible(UVeVisible) spectroscopies. The structural and vibrational properties for dieldrin in gasphase and in aqueous solution were computed combining those experimental spectra with hybridsB3LYP and WB97XD calculations by using the 6-31G* and 6-311þþG** basis sets. Here, the experimentalavailable Hydrogen and Carbon Nuclear Magnetic Resonance (1H and 13C NMR) for dieldrin were alsoused and compared with those predicted by calculations. The B3LYP/6-311þþG** method generates themost stable structures while the results have demonstrated certain dependence of the volume and dipolemoment values with the method, size of the basis set and, with the studied media. The lower solvationenergy for dieldrin (32.94 kJ/mol) is observed for the higher contraction volume (2.4 Å3) by using theB3LYP/6-31G* method. The NBO studies suggest a high stability of dieldrin in gas phase by using theWB97XD/6-31G* method due to the n/p* and n*/p* interactions while the AIM analyses support thishigh stability by the C18/H26 and C14/O7 contacts. The different topological properties observed inthe R5 ring suggest that probably this ring plays a very important role in the toxics properties of dieldrin.The frontier orbitals show that when dieldrin is compared with other toxics substances the reactivityincreases in the following order: CO < STX < dieldrin < C6Cl6 <TCAB < TCAOB < CN where evidently, thepresence of five rings and six Cl atoms decrease the reactivity of dieldrin, as compared with hexachlorobencene.The WB97XD method and the two basis sets predicted for dieldrin in both media lowreactivities, higher nucleophilicity and, low electrophilicity. All the bands observed in the IR and Ramanspectra were completely assigned to the 75 vibration normal modes and their harmonic force fields andforce constants for first time are reported for dieldrin. The predicted FTIR, FT-Raman, UVeVisible and 1Hand 13C NMR spectra for dieldrin show a reasonable concordance with the experimental ones.