Organic Nitrogen Compounds and Biomolecules
Organic Nitrogen Compounds and Biomolecules tests amines, diazonium salts, amides and the structure and function of carbohydrates, proteins, enzymes, vitamins and nucleic acids. Basicity order and biomolecule classification are high-yield.
Amines and diazonium salts
- Amines are classified as 1°, 2° or 3° by the number of carbon groups on nitrogen.
- Basicity in water: (CH3)2NH > CH3NH2 > (CH3)3N > NH3; aniline is much weaker because the lone pair is delocalised into the ring.
- Aniline reacts with NaNO2/HCl at 0–5 °C to give benzenediazonium chloride.
- Diazonium salts undergo Sandmeyer reactions (CuCl/HCl gives chlorobenzene) and coupling with phenol to give azo dyes.
Biomolecules
- Monosaccharides cannot be hydrolysed; reducing sugars have a free aldehyde or ketone group.
- Amino acids join by peptide bonds; the primary structure is the sequence of amino acids.
- Enzymes are biological catalysts, highly specific and usually proteins.
- DNA contains deoxyribose and bases A, T, G, C; RNA contains ribose and U instead of T.
Worked example
Arrange cyclohexylamine, ammonia and aniline in increasing order of basicity in water. Reasoning: cyclohexylamine has an electron-donating cyclohexyl group and no resonance delocalisation, so it is the strongest. Ammonia is next. Aniline’s lone pair is delocalised into the benzene ring, making it the weakest. Order: aniline < ammonia < cyclohexylamine.
Traps
- Do not assume 3° amines are always the most basic in water; solvation matters.
- Diazotisation must be kept at 0–5 °C to avoid decomposition.
- All monosaccharides are not reducing sugars; sucrose is non-reducing.
- A peptide bond is an amide bond, not an ester bond.