In this lesson, we will learn:
- The names and structures of more major functional groups in organic chemistry.
- The naming priority of the major functional groups in organic chemistry.
- How to apply IUPAC systematic naming and priorities to more complex organic compounds.
- This lesson covers some more functional groups commonly seen in organic chemistry. There is a huge number of recognized organic functional groups, but the most common are acylic groups containing O and N with some variation in the number of bonds to carbon being made.
- As already seen in our lessons covering the key functional groups, the following steps should be done in order when naming organic compounds:
When naming compounds containing multiple functional groups, the highest priority functional group takes the suffix and the priority in numbering the carbon chain.
- Identify the longest continuous carbon chain.
- Identify the functional groups in the molecule.
- Identify the highest priority functional group, and number the carbon chain starting there (if this group isn't at an end of the chain, start numbering at the chain end which gives the priority group the lowest possible numbering).
- Give the highest priority functional group the suffix of the compound name.
- All other functional groups can be numbered alphabetically once the highest priority group has the suffix and the carbon chain is numbered.
Naming aromatic compounds is not clear-cut. There is no ruleset that will always find the best name for an aromatic compound because the old pre-IUPAC names (which are not systematic) are still in use and often preferred to the new IUPAC name. However, the following is a sensible ruleset that will lead you to a recognized name for aromatic organic compounds:
- One partial exception to this is in compounds containing both alkenes and alkynes, or "enynes". The alkene is higher priority and is numbered lower, but the alkyne takes the suffix in enynes.
The following functional groups are listed according to their priority, highest first, in the naming of organic compounds:
- Treat a benzene ring as a "6-carbon alkene" group – remember benzene's own IUPAC name: 1,3,5-cyclohexatriene!
- Treat groups below alkenes as lower priority – alkynes, alkanes, ethers, halogens and nitro groups. With just these, the suffix will be – benzene.
- Treat any carbon chain longer than 6 carbons and groups higher than alkenes as higher priority to the benzene ring – it will take the prefix phenyl- here.
Key for the table:
R, R', R'' = can be any alkyl or aromatic group.
X = halogen (F, Cl, Br, I)