Applications of 15N NMR spectroscopy to the study of unsymmetrically N‐substituted amides and model peptide compounds

Abstract

Abstract13C and 15N spectra of unsymmetrically N‐substituted formamides and alkyl‐, substituted alkyl‐, and arylcarboxamides, which can be considered as model peptide compounds, were determined and discussed in terms of nitrogen lone pair delocalization. Differential solvent shifts and through‐space steric effects are considered as a tentative explanation of the difference in screening between geometrical diastereoisomers. Z‐E assignment and the thermodynamic stability of diastereoisomers can also be predicted in some circumstances from a consideration of the 15N chemical shifts. Data concerning small peptides are discussed in the light of the results obtained using the model compounds.