Carboxylic acid
The carboxylic acid has the -COOH group (carbonyl + hydroxyl on the same carbon) at the end of the chain. It's the highest-priority functional group in IUPAC nomenclature — if present, it always becomes the name's suffix, never a prefix.
General formula
Naming rule
Name = acid + main chain (including the -COOH carbon) + suffix -oic acid. No locant needed — the -COOH is always at position 1.
How to name it with IUPAC
Use this sequence to move from the structure to the systematic name:
- Include the carboxyl carbon in the parent chain; it is C1.
- Write “-oic acid” after the parent root.
- CH₃CH₂COOH = propanoic acid: three carbons including the carboxyl carbon.
Examples
| Name | Formula |
|---|---|
| Methanoic acid (formic) | HCOOH |
| Ethanoic acid (acetic) | CH₃COOH |
| Propanoic acid | C₂H₅COOH |
| Benzoic acid | C₆H₅COOH |
Visual examples
See how the functional group appears inside the chain. Compare the drawings with the formulas in the table to practice visual recognition.
Chemical reading
The carboxyl combines C=O and OH. Resonance stabilizes its conjugate base, making it more acidic than an alcohol.
Properties and applications
Acetic acid is in vinegar and fatty acids occur in oils and fats; short chains form strong hydrogen bonds.
- A base gives a carboxylate and an alcohol gives an ester. The COOH carbon is always C1.
- Compare polarity, chain size, and hydrogen bonding before predicting physical properties.