Amides nuclear magnetic resonance spectra

This difference in the AG values is especially observable in the temperature-dependent, nuclear magnetic resonance spectrum of 5,6-bis(acetamido)-l,6-anhydro-5,6-dideoxy-j8-L-idopyranose. This sugar contains a flve-membered and a six-membered ring amide in... 

Protonation of simple amides has been found to markedly decrease the double bond character of theC—N amide linkage. Thus Berger, et al. (1959) foimd that protonation of the C—N bond in iNT-methylacetamide and iV,AT -dimethylacetamide resulted in a depression of the double bond character as measured by nuclear magnetic resonance. In neutral aqueous solution the nuclear magnetic resonance spectrum shows the presence of two iV-methyl lines indicating the absence of free rotation about the C—N linkage. In the presence of acid the doublet is replaced by a single absorption band with the onset of free rotation. 

Then, with the help of a colleague, Asher Mandelbaum, at the Technion in Haifa, we got a high-resolution mass spectrum, which indicated that the molecule contains a nitrogen, certainly not a common feature in fatty acids. However, the structure was now close at hand. Some more mass spectra and a better nuclear magnetic resonance (NMR) led to a final formulation of the ligand as arachidonoyl ethanol amide (Devane, Hanus, et al., 1992). 

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