Computational NQR−NBO Parameters and DFT Calculations of Ampicillin and Zwitterion (Monomer and Dimer Structures)

Density functional theory (DFT) was used to analyze the structure and Nuclear quadrupole coupling constants (NQCC), χ, and asymmetry parameters, η, of 14N nuclei have been calculated for the antimicrobialampicillin in monomeric and their dimers using B3LYP/6-311G(d) method on the differences between the structural parameters in monomeric and their dimers states in the gas phase. For this purpose, electric field gradient (EFG) at the sites of quadrupole nuclei and resonance interactions have been calculated and evaluated for each compound. Additionally, it could be observed that the factor of resonance interaction which is not the only effective factor on values and trend of NQR parameters changes by passing of monomeric state to other ones. It was also found that conformation plays a very effective role in the determination of the values of the calculated NQCC parameters. Sensitivity of the NQR parameters to the changes in the conformational structure is significantly greater than that of the changes in the other structural parameters such as bond lengths.