Hydrogen Bonds of Peptide Group in Four Acetamide Derivatives:DFT Study of Oxygen and Nitrogen NQR and NMR Parameters

A computational study was conducted to examine hydrogen bond (HB) properties of peptide group in four derivatives of acetamide by density functional theory (DFT) calculations of nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) parameters at the sites of oxygen and nitrogen nuclei of peptide groups. The available crystalline structures of four derivatives; 2,2,2-trifluoro-N-(2-hydroxy-5-nitrophenyl)acetamide, N-(2-acetylphenyl)acetamide, 2-chloro-N-(4-nitrophenyl) acetamide, and N-(4-fluorophenyl)acetamide were obtained from literature. Following the influence of HB interactions, calculations were done on non-hydrogen bonded (single) and hydrogen bonded (cluster) models of derivatives. The results revealed differet behaviors of peptide group in contributing to HB interactions in different derivative structures. HB interactions are the strongest in 2-chloro-N-(4-nitrophenyl)acetamide. However, the strengths of HB interactions in all of the four derivatives are still less than that of acetamide. The calculations are done at the level of B3LYP method and 6-311++G** standard basis set using GAUSSIAN 98 package of program