Form and split amide links with pH-appropriate products.
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Method and worked examples
An amide contains a carbonyl carbon bonded directly to nitrogen: –C(=O)–N–. It is different from an amine, whose nitrogen is not attached directly to a carbonyl carbon. A condensation model combines a carboxylic acid and an amine, removes water and joins the carbonyl carbon to nitrogen. Heating or suitable activation is required; simply mixing the reactants can instead form an ammonium carboxylate salt.
A dicarboxylic acid and a diamine can form a polyamide, while an amino acid can link to itself. Hydrolysis breaks the C–N amide bond. Acidic conditions give a carboxylic acid and a protonated amine; alkaline conditions give a carboxylate and an uncharged amine. Strong hydrogen bonding between many polyamide chains contributes to fibre strength and relatively high melting temperatures.
Example 1
Identify the reactants corresponding to CH3CONHCH2CH3 in a condensation model.
The carbonyl fragment comes from CH3COOH and the nitrogen fragment from CH3CH2NH2. Removing H2O links them to form the amide.
Example 2
Give products of alkaline hydrolysis of CH3CONHCH3.
The C(=O)–N bond splits, giving CH3COO− and CH3NH2. Water/OH− supplies the groups needed to complete the products.
Watch out:An amide nitrogen is directly bonded to a carbonyl carbon; that carbonyl changes its chemistry.
Amide links and hydrolysis products practice | Year 12 Chemistry | Ascent Arcade