Naming a compound
A formula is a picture. A name is a word a chemist can say aloud.
Step 1 of 4
- Count the carbons: four. The stem is but.
- The chain has single bonds: butane.
- The group –COOH gives the ending –oic acid.
- Drop the final e of butane. The name is butanoic acid.
Loading lab…
Read the structure. Pick the stem and the ending.
The rule
The stem tells the number of carbons. The ending tells the group. Drop the final e before an ending that starts with a vowel.
The stem is the front of the name. The ending comes last.
A prefix goes before the stem, as chloro- does in chlorobutane.
Meth, eth, prop and but mean 1, 2, 3 and 4 carbons. Pent and hex mean 5 and 6. A double bond changes -ane to -ene. A triple bond changes it to -yne.
For CH₃–CH₂–OH, 2 carbons give eth. Single bonds give ethane. The –OH group gives -ol. Drop the final e, and the name is ethanol.
| Group | Ending or prefix | Example |
|---|---|---|
| –OH, alcohol | ending -ol | butanol |
| –CHO, aldehyde | ending -al | butanal |
| C=O inside the chain, ketone | ending -one | butanone |
| –COOH, carboxylic acid | ending -oic acid | butanoic acid |
| –Cl, a chlorine group | prefix chloro- | chlorobutane |
| –Br, a bromine group | prefix bromo- | bromohexane |
Watch out!
Count the carbon in –COOH and –CHO too. In CH₃–CH₂–COOH there are three carbons, not two.