Aldehyde
An aldehyde has the carbonyl group (C=O) mandatorily at the end of the chain — the carbonyl carbon also carries a hydrogen (except in methanal, where it carries two). This differentiates it from a ketone, whose carbonyl sits in the middle of the chain.
General formula
Naming rule
Name = main chain (counting the carbonyl carbon) + suffix -al. No locant needed — the aldehyde carbonyl is always at position 1 by definition.
How to name it with IUPAC
Use this sequence to move from the structure to the systematic name:
- Include the -CHO carbon in the parent chain; it is always C1.
- Use the -al suffix; locant 1 does not need to be written.
- CH₃CH₂CHO = propanal: three carbons and a terminal aldehyde.
Examples
| Name | Formula |
|---|---|
| Methanal (formaldehyde) | HCHO |
| Ethanal (acetaldehyde) | CH₃CHO |
| Propanal | C₂H₅CHO |
| Benzaldehyde | C₆H₅CHO |
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 carbonyl is at the end of the chain and the carbonyl carbon bears H, making aldehydes easy to oxidize.
Properties and applications
Methanal is used in resins, ethanal is an industrial intermediate, and aromatic aldehydes occur in fragrances.
- Oxidation gives a carboxylic acid and reduction gives a primary alcohol. CH₃CH₂CHO is propanal.
- Compare polarity, chain size, and hydrogen bonding before predicting physical properties.