What are the rules for naming compounds with multiple identical groups?

Compounds with multiple identical groups are named using prefixes to indicate the number of each group.

When naming compounds with multiple identical groups, prefixes are used to denote the number of each group present. These prefixes are derived from Greek and are as follows: 'mono' for one, 'di' for two, 'tri' for three, 'tetra' for four, 'penta' for five, 'hexa' for six, 'hepta' for seven, 'octa' for eight, 'nona' for nine, and 'deca' for ten.

For example, a molecule with two chlorine atoms would be named 'dichloro', while a molecule with three methyl groups would be named 'trimethyl'. It's important to note that the prefix 'mono' is often omitted when naming the first element in a binary compound.

In addition to using prefixes, the groups are also listed in alphabetical order in the compound name. This is regardless of the number of atoms in each group. For instance, in the compound dichloropentane, 'chloro' comes before 'pentane' in the name, even though there are more carbon atoms in the pentane group than chlorine atoms in the dichloro group.

Furthermore, when the compound is a ring structure, the term 'cyclo' is added before the name of the compound. For example, a six-carbon ring with two chlorine atoms would be named '1,2-dichlorocyclohexane'. The numbers '1,2' indicate the positions of the chlorine atoms on the ring.

Lastly, it's crucial to remember that the rules for naming compounds are standardised by the International Union of Pure and Applied Chemistry (IUPAC). This ensures that every compound has a unique and universally accepted name.