Chapter 8 · Chemistry
The Carboxyl Group: Structure and Naming
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What –COOH really is: a carbonyl and a hydroxyl on one sp² carbon, joined by resonance that makes the carbon less electrophilic than in aldehydes; and how carboxylic acids get their common and IUPAC names.
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Preparing Carboxylic Acids: Four RoutesFour ways to make a carboxylic acid: oxidising primary alcohols and aldehydes, oxidising alkylbenzenes, hydrolysing nitriles and esters, and adding a Grignard reagent to dry ice, which adds one carbon (mechanism with curved arrows).Chemistry
Key points
- –COOH = a carbonyl (C=O) + a hydroxyl (–OH) on one carbon: carb-oxyl.
- The carboxyl carbon is sp²: planar, bonds about 120° apart.
- Resonance: an –OH lone pair moves toward C while the C=O pair moves onto O, so the carbon is less electrophilic than in aldehydes and ketones (no nucleophilic addition).
- Common names come from the source: formic (formica, ant), acetic (acetum, vinegar), butyric (butyrum, butter).
- IUPAC: alkane − e + oic acid; the COOH carbon is C-1; two COOH groups keep the e (ethanedioic acid).
Resonance in the carboxyl group
R–C(=O)–OH ⟷ R–C(–O⁻)=O⁺–H
One curved arrow takes a lone pair of the –OH oxygen into the C–O bond; another takes the C=O π pair onto the carbonyl oxygen. The carbon's δ⁺ is partly made up, so it is less electrophilic than the carbonyl carbon of an aldehyde.
Names
| Formula | Common name (source) | IUPAC name |
|---|---|---|
| HCOOH | formic acid (formica, ant) | methanoic acid |
| CH₃COOH | acetic acid (acetum, vinegar) | ethanoic acid |
| CH₃CH₂COOH | propionic acid | propanoic acid |
| CH₃CH₂CH₂COOH | butyric acid (butyrum, butter) | butanoic acid |
| (CH₃)₂CHCOOH | isobutyric acid | 2-methylpropanoic acid |
| HOOC–COOH | oxalic acid | ethanedioic acid |
| C₆H₅COOH | benzoic acid | benzoic acid |
- Replace the final -e of the alkane by -oic acid.
- Number from the COOH carbon (C-1).
- Two COOH groups: keep the -e, add -dioic acid.
Quick quiz
5 questions. Choose an answer for each, then submit to see your score and the explanations.
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