Structure, properties and preparation2 concepts
Carboxyl group, series and properties
3× asked, last 2024sp² carboxyl C. H-bonded dimers persist even in vapour. C1–C4 acids mix with water; solubility falls as the chain grows.
| n | CₙH₂ₙ₊₁COOH | Formula | Homologue |
|---|---|---|---|
| 0 | methanoic acid | CH₂O₂ | first |
| 1 | ethanoic acid | C₂H₄O₂ | second |
| 2 | propanoic acid | C₃H₆O₂ | third |
| 3 | butanoic acid | C₄H₈O₂ | fourth |
Formulas from the structures: the series starts at n = 0.
| Named “acid” | –COOH groups on the structure |
|---|---|
| picric acid | 0 |
| carbolic acid | 0 |
| oxalic acid | 2 |
| citric acid | 3 |
Counted on each structure: picric and carbolic acids are phenols.
391ethanoic acid370propan-1-ol329propanone322propanalb.p. (K)
- Not acetic acid as the first member. The series starts at (). So () is the second homologue and the third.
- Not every 'acid' by name has –COOH. Check the structure: picric acid is a trinitrophenol. Count only true –COOH groups.
Preparation of carboxylic acids
2× asked, last 2025Any side chain with a benzylic H becomes –COOH; tert-butyl is not oxidised. Mild hydrolysis of a nitrile stops at the amide.
| Start + reagent | C in | Acid formed | C change |
|---|---|---|---|
| CH₃CH₂CH₂MgBr + CO₂ | 3 | +1 | |
| butanone + I₂/NaOH | 4 | −1 | |
| propanenitrile + H₃O⁺ | 3 | 0 | |
| 1,1,1-trichloropropane + OH⁻ | 3 | 0 | |
| methyl propanoate + H₃O⁺ | 3 | 0 | |
| propylbenzene + hot KMnO₄ | 9 | −2 |
Acids made from each structure (the ester’s OCH₃ carbon leaves as CH₃OH and is not counted). Side-chain oxidation keeps only the benzylic carbon; tert-butylbenzene has no benzylic H and is not oxidised.
- Not an acid from every route. PCC (from ) and Stephen (, then ) stop at the aldehyde; mild hydrolysis of RCN stops at the amide.
- Quick method. Count carbons first: Grignard + adds one C, haloform removes one, hydrolysis of –CN, or an ester keeps the count. + gives butanoic, not propanoic, acid.
Also remember
- Uses: in rubber, textile, dyeing, leather and electroplating; as solvent and vinegar; hexanedioic acid for nylon-6,6; sodium benzoate as food preservative; higher fatty acids for soaps and detergents.
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10 more concepts in 2 topics
Acidity of carboxylic acids and Reactions of acids and their derivatives. Read the first part free. Sign in free with Google to read the rest and download the PDF.
Acidity of carboxylic acids4 concepts
- Acidity and the NaHCO₃ test2×
- Substituent effects in aliphatic acids
- Benzoic acids and the ortho effect1×
- Ring substitution of benzoic acid
Reactions of acids and their derivatives6 concepts
- Fischer esterification2×
- Acid chlorides, anhydrides and amides1×
- Reduction to primary alcohols1×
- Decarboxylation, Kolbe and HVZ
- Reactivity toward acyl substitution1×
- Esters with Grignard reagents1×
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