The Rotational and Configurational Isomerism of N-(Monosubstituted ethyl)amides by Nuclear Magnetic Resonance

Abstract

Several N-(monosubstituted ethyl)amides were synthesized and their carbon and proton nuclear magnetic resonance (¹³C and ¹H-NMR) spectra were determined. Both (Z) and (E) stereoisomers could be observed in the formamides, but only the (Z) isomer was identified in the acetamides and phenylacetamides. The main body of the ¹H-NMR results indicated that the methylene protons were equivalent. This finding is interpreted in terms of free rotation around the -CH₂-CH-bond and magnetic equivalence. In cases where the ¹H-NMR spectra revealed and ABX pattern, an interpretation is offered based on different populations among "pure staggered"conformers.