amide
/ AM-ide /
Every protein in your body is held together by amide bonds. Nylon is a chain of amide bonds. The pain reliever in paracetamol contains an amide. This single linkage — a carbonyl bonded to a nitrogen — is one of the most important in all of chemistry and biology, because it is both strong and stable.
An amide has the structure R-CO-NR'2, where the carbonyl carbon (C=O) is bonded to a nitrogen carrying hydrogens or carbon groups. Here is the subtle and crucial point: the nitrogen's lone pair of electrons delocalizes into the carbonyl by resonance, so the C-N bond gains partial double-bond character. This has two big consequences. First, the amide is flat and rigid around that bond and rotation is hindered — the very feature that gives proteins their defined shapes. Second, with the nitrogen's electrons busy stabilizing the carbonyl, amides are the least reactive of the common acyl derivatives, and the amide nitrogen is a far weaker base than an ordinary amine.
Amides are made from a more reactive derivative (an acyl chloride or anhydride) plus an amine, or with difficulty by heating a carboxylic acid with an amine. Their stability is exactly why they are everywhere structural: the peptide bond linking amino acids is an amide, and synthetic polyamides like nylon and Kevlar owe their toughness to it. Because amides resist hydrolysis, breaking them apart usually demands strong acid or base and heat, or specialized enzymes in living systems.
Acetamide is CH3-CO-NH2. In a protein, the amide (peptide) bond -CO-NH- repeats down the backbone; resonance keeps each unit flat, which is why proteins fold into precise, reproducible shapes.
The amide bond is the stable, flat linkage behind proteins and nylon.
An amide nitrogen is a weak base, not a strong one like an ordinary amine — its lone pair is tied up in resonance with the carbonyl. So amides are barely protonated under conditions that would readily protonate an amine.