- Locate the longest continuous chain of carbon atoms. Remember that the longest chain may be bent.
- Number your chain from the end nearest a double or triple bond, otherwise from the end with the closest branch.
- Use Greek numerical prefixes to find the "parent name" of your compound. This is based on the size of your longest chain. For example, if you have a C6 (6-carbon chain) molecule, it is considered a hexane. C7 is heptane, C8 is octane, and so on. These are all alkanes (single bonds only).
Alkenes: If the chain contains a double bond end the name with -ene. For example, a C9 containing a double bond is a nonene. Place the number of the adjacent carbon in front of the name.
Ex: CH2=CHCH2CH3 is but-1-ene. OR Simply butene, because, generally 1 is ommited .
Alkynes: If the chain contains a triple bond end the name with -yne. For example a C5 containing a triple bond is a pentyne.
Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a". Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond.
Ex: CH2=CHCH=CH2 is 1,3-butadiene.
- Name your side chains. They are named for the carbon on the main chain to which they are attached. For example, if you have a C1 compound attached to the second carbon in the chain, it is called a 1-methyl group (use the same prefixes as above). If there is more than one of the same group, add the number of the carbon of attachment to the name. Using the previous example with the addition of a methane on the the third carbon as well, you would name it a 1,3-dimethyl group. Prefixes for groups:
- Arrange your side chains in alphabetical order and tack them on before your parent name. Complex side chains go in parentheses.
- Keep practicing! Before you know it, you'll be able to name or draw a 1,2-di(1,2 dimethyl ethyl) cyclopentane with ease!
Watch out for rings. They are named for the number of carbons in the central ring; for example, a 5-carbon ring is a cyclopentane.
C1 through C4 compounds do not follow the prefix naming rule. C1 is methane, C2 is ethane, C3 is propane, and C4 is butane.
Many compounds are called by their common names instead of using the new IUPAC system. For example, a side chain that would be named under the IUPAC system as (1-methylethyl) is also known as an isopropyl group. Be careful not to mix your naming systems. 12 April 2011Comment