What are the naming rules for bicyclic compounds?

Bicyclic compounds are named based on the number of carbon atoms in the rings and the number of shared atoms.

In more detail, the naming of bicyclic compounds follows specific rules set by the International Union of Pure and Applied Chemistry (IUPAC). The first step is to identify the parent chain, which is the longest continuous chain of carbon atoms. This chain may include one or both rings of the bicyclic compound. The parent chain is then named according to the number of carbon atoms it contains, using the standard prefixes for organic compounds (meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non-, dec-, etc.).

Next, the number of carbon atoms in each ring is identified. If the rings are of different sizes, the larger ring is given priority. The number of carbon atoms in the rings is indicated by a prefix (di-, tri-, tetra-, penta-, hexa-, etc.) before the word 'cyclo'. For example, a compound with two rings of six carbon atoms each would be named 'dicyclohexane'.

The number of shared atoms between the rings is also important. This is indicated by a set of numbers in brackets after the 'cyclo' part of the name. The numbers represent the number of carbon atoms in the bridge (the part of the molecule connecting the two rings), with the largest number listed first. For example, a compound with two rings of six carbon atoms each, connected by a bridge of two carbon atoms, would be named 'dicyclo[2.2.2]octane'.

Lastly, any substituents (groups of atoms attached to the parent chain) are named and their positions indicated. The carbon atoms in the parent chain are numbered starting from the end closest to the first substituent. The names of the substituents are then added as prefixes to the name of the parent chain, in alphabetical order, with their positions indicated by the corresponding numbers.