What if the hydrocarbon chain has a branch?
The name for a given alcohol structure 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
3-methylpentan-2-ol
eth - 2 carbons
prop - 3 carbons
but - 4 carbons
pent - 5 carbons
hex - 6 carbons
3-methylpentan-2-ol
- The ending for alcohols is -ol
- The stem in the name depends on the number of carbons in the longest chain containing the carbon bearing the OH.
In the alcohol at the right, the longest chain including the carbon bearing OH has five 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.
Note that saturated hydrocarbon substituents have the same name as the parent alkane except with ane substituted by -yl. - The functional group determines the numbering of the chain.
In an alcohol, the carbon bearing OH has the lowest possible number.
Carbon 1 can be at either end of the chain. In the example above carbon 1 is at the right-hand side.
If the OH had been at a different position, carbon 1 may have been on the left-hand side.