The name for a given aldehyde or ketone has three parts: prefix(es) stem ending
meth - 1 carbon
eth - 2 carbons
prop - 3 carbons
but - 4 carbons
pent - 5 carbons
hex - 6 carbons
2-methylbutanal
3-methylbutan-2-one
eth - 2 carbons
prop - 3 carbons
but - 4 carbons
pent - 5 carbons
hex - 6 carbons
2-methylbutanal
3-methylbutan-2-one
- The ending for aldehydes is -al. The ending for ketones is -one.
- The stem used in the name depends on the number of carbons in the longest chain containing the carbonyl carbon
In the aldehyde and ketone examples shown, the longest chain including the carbonyl group has four carbon atoms.
- Substituents on the longest chain are included in the name as prefixes.
Any atom or group of atoms replacing H at a carbon is called a substituent.
Some common substituents are shown below.
bromo Br– methyl CH3– chloro Cl– ethyl CH3CH2–
For compounds where two substituents of the same type are on the same carbon, the prefix di- is used and the locator before it becomes n,n where n is the number of the carbon on which the identical substituents are found.
The two examples both have methyl substituents.
- The functional group determines the numbering of the chain.
The carbonyl group is always given the lowest possible number.
This means that for an aldehyde the carbonyl carbon is number 1, and the number of the carbonyl carbon is not shown.
Carbon 1 can be at either end of the chain. In the example above carbon 1 is at the right-hand side.