Organic Chemistry: Structure, Nomenclature and Functional Groups
What this domain tests
Naming organic compounds systematically, recognising functional groups, and identifying isomers.
Core rules
- Find the longest carbon chain containing the principal functional group; number to give that group the lowest locant, then give substituents the lowest locants.
- Suffix priority: carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene/alkyne > halogenoalkane.
- Isomerism types: chain, position, functional group, geometric (E/Z, cis–trans) and optical (a chiral carbon bearing four different groups).
- Displayed, structural, skeletal and general formulae show different information; the molecular formula shows only atom counts.
Worked example
Name CH3CH(CH3)CH2CH(OH)CH3. The longest chain containing OH has five carbons. Numbering must give the OH the lower locant (2), even though that places the methyl at 4 rather than 2. The name is 4-methylpentan-2-ol. The suffix group outranks substituents when choosing the direction of numbering.
Traps
Numbering from the end that gives substituents the lowest number while ignoring the suffix group; choosing a shorter chain because it looks straighter; calling a C=C cis or trans when one carbon carries two identical groups; confusing aldehydes and ketones in condensed formulae such as CH3COCH3.