Introductory IUPAC Organic Nomenclature

What's in a name?

The IUPAC name of an organic molecule is assembled from components that describe various features of the molecule.

Functional group suffix
This is added to the end of the name based on the principal functional group.

Root
This defines the number of atoms (usually carbon atoms) in the longest continuous chain that contains the principal functional group.

Substituent prefix
Any groups other than the principal functional group are substituents and are added to the beginning of the name in alphabetical order.

Multiplier
If a group occurs more than once, a simple multiplier (e.g. di, tri, tetra, etc.)  is used to indicate how many times it occurs.

Locants
Locants are numbers (or occasionally letters) that define the position of the principal functional group and substituents.  Typically there needs to be a locant for each functional groups and each substituent.

The basic structure of the IUPAC name is shown schematically below :

Let's work through the example shown - we will expand on the details in the pages ahead.
the principal functional group is an alcohol, so the suffix  -ol is required
the longest continuous chain with the -OH attached is C5 and an alkane so we have a pentane system
there are two substituents, both methyl groups, hence dimethyl
the -OH is on C2 so we have a -2-ol
the methyl groups are on C3 and C4, so we have a 3,4-dimethyl
hence : 3,4-dimethylpentan-2-ol Note :  the pentan-2-ol could also be written as 2-pentanol

©Dr. Ian Hunt, Department of Chemistry