Chapter 8 · Chemistry
Aldehyde or Ketone? Structure and IUPAC Names
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Methanal and propanone both have C=O, yet one is an aldehyde and one a ketone. Where the C=O sits decides it, and the names follow: -al for aldehydes, -one for ketones, plus the common names.
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Making Aldehydes and Ketones: Methods and Named ReactionsFour routes make both aldehydes and ketones (from alcohols, alkenes and alkynes); named reactions make only one: Rosenmund, Stephen, Etard and Gatterman-Koch for aldehydes; Grignard on nitriles, dialkylcadmium and Friedel-Crafts acylation for ketones.Chemistry
Key points
- Aldehyde: an H on the carbonyl carbon, so C=O sits at the end of the chain (R–CHO).
- Ketone: carbon groups on both sides, so C=O sits inside the chain (R–CO–R′).
- IUPAC: alkane − e + al (methanal, ethanal, propanal; the CHO carbon is C-1, no locant); alkane − e + one (propanone, butanone, pentan-2-one, pentan-3-one).
- Common names: formaldehyde, acetaldehyde; dimethyl ketone = acetone. The smallest ketone, propanone, has three carbons.
Aldehyde or ketone
| Aldehyde | Ketone | |
|---|---|---|
| On the carbonyl C | at least one H | two carbon groups |
| Position of C=O | chain end | inside the chain |
| IUPAC ending | -al | -one |
| Smallest | methanal (1 C) | propanone (3 C) |
Names
| Formula | IUPAC | Common |
|---|---|---|
| HCHO | methanal | formaldehyde |
| CH₃CHO | ethanal | acetaldehyde |
| CH₃COCH₃ | propanone | acetone (dimethyl ketone) |
| CH₃COCH₂CH₃ | butanone | ethyl methyl ketone |
| CH₃CH₂COCH₂CH₃ | pentan-3-one | diethyl ketone |
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