- To name cyclic hydrocarbons, add cyclo- before the root
Cyclic hydrocarbon nomenclature follows the same basic format as simple hydrocarbon nomenclature (repeated below) except the size of the ring is used as the root and the prefix `cyclo`is inserted after the branching substituents. For substituents, number around the ring such that the lowest numbers are used in the name.
Review: Hydrocarbon nomenclature rules:
- Find the longest continuous chain of carbon atoms. This chain determines the parent name (root) of the alkane.
- Identify the suffix for the root.
- Number the chain beginning at the end of the chain nearest any branching, thus obtaining the use of lower numbers in the name.
- The root of each substituent is the longest chain of carbons in the branch. Substituent alkyl groups are referred to with suffix “-yl”.
- If an alkyl group appears more than once, use the prefixes: di, tri, tetra, penta, hexa, etc.
- Complete the name. Use these numbers to designate the location of the substituents groups. Numbers are separated from letters by dash (-) and two numbers are separated by a comma (,). If two or more substituents are present on the same carbon atom, use the number twice. List the groups alphabetically (alphabetize based on the root group from step 4, not the prefixes from step 5).
To name unbranched cyclic hydrocarbons, the root is determined by the total number of atoms in the ring. In the example below, there are six atoms, making the root “hex”. Following the format above, the name of this molecule is cyclohexane.
Substituted cyclic hydrocarbons are named analogously to acyclic hydrocarbons. The only difference is rule 3 needs to be modified to obtain the lowest numbers in the name. In the example below, the indicated numbering scheme is the only one that minimizes the substituent numbering. The rest of the name, “1,2,4-trimethylheptane”, follows standard IUPAC rules.
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