Simple Theoretical Structural Studies and Mathematical Correlations of Amide Bond Resonance Forms with IRVibration Frequency Data in Amides

Some of the properties in amides are related to the number of nitrogen lone-pair electrons andcarbonyl group delocalization. There is a significant amount of electron delocalization inamides, with lone-pair electron donation to the π–system of the carbonyl (C=O) group. In thisstudy, was proposed a quantitative model concerning the amide resonance contribution forms,which used vibration frequencies (or wave numbers) of appropriate bonds. The vibrationalfrequencies of C=O and –CN– bonds in the two forms of amide bonds in 1-30 were calculatedby the DFT-B3LYP/6-31G* method. The B3LYP calculation results were utilized to constructa model to calculate the polar and resonance percentages of amide bonds. The solvent (acetone,CHCl3, Et-OH and CCl4) effects on the resonance and polar percentages of amides wereinvestigated by the results of the model.

Keywords:

Amide bond , Resonance forms , IR-Spectroscopy , Stretching vibration frequency , B3LYP method