Naming a compound
Show on a big screenA formula is a picture. A name is a word a chemist can say aloud.
- 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.
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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.
Try the lab to finish this lesson.