[uglepik]

I have made a couple of compounds with amide bonds, both primary and secondary amides (peptide backbone cleaved from rink amide resin). But when I run proton-NMR I don't seem to see the nitrogen-bound protons at all. My solvent is chloroform, sometimes with added acetic acid (both deuterated).

Can anybody tell me if this is normal?

[Dan]

Amide NHs can exchange readily - the pKa of acetamide is ~17 (so about the same as isopropanol).

I've made a few secondary amides in the past and I could see the NH in CDCl₃, but not in D₂O. Adding acetic acid-d₄ will cause rapid exchange I expect, and depending on the concentration and dryness of the sample you may not see them in CDCl₃ either (just like alcohols).