Theoretical studies of ethylnitrolic acid using Gaussian

The tautomerism of all possible forms of ethylnitrolic acid was investigated theoretically in various environment including gas phase, ethanol, dimethyl sulfoxide (DMSO) and water. The calculations were carried out at DFT/B3LYP and MP2 of theory singly. It was found that, form of B eythynitrolic acid is the most stable isomer in the both gas phase and solvent. The activation energies for conversion of A to R and B to A in the gas phase and solvent using two methods DFT/B3LY and MP2 were obtained. For conversion of A to R, the activation energies are 62.24 and 44.10 kcal/mol in the gas phase and water respectably according DFT method. Vibrational analysis was done to obtain vibrational frequencies and these values were compared to experimental data. Geometrical parameters of three isomers, A, B and R, were calculated using two methods (DFT/B3LYP and MP2) in the gas phase and solvent. It can be said, that environment can affect very small on the geometrical parameters. Acidity constants (PKa) of two isomers (A and R) were calculated in the gas phase and water using DFT/B3LYP and MP2. After that, these quantities were evaluate with experimental values and it was determined that DFT/B3LYP is more accurate method to obtain PKa.

Keywords:

Tautomerism , ethylnitrolic acid , solvent effect , proton transfer reaction , acidity constant , DFT , B3LYP and MP2