C and '"N 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 geomelrical diastereoisomers.
2-E assignment and the thermodynamic stability of diastereoisomers can also be predicted in somecircumstances 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.
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