Give every carbon an address.
Find the longest appropriate chain containing the principal functional group or multiple bond. Number it to give that feature its lowest permitted locant, then place and name substituents. Common roots run meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non-, dec-.
CH₃CH(OH)CH₂CH₃ is butan-2-ol. CH₃COCH₂CH₃ is butan-2-one. A terminal –CHO gives an aldehyde name ending -al. For esters, name the alcohol-derived alkyl group first, followed by the acid-derived alkanoate.
Primary, secondary and tertiary describe how many other carbon atoms attach to the carbon bearing OH or the halogen. They do not describe the total number of carbon atoms in the molecule.
Spot the functional group
Condensed structural diagrams. Bonds show connectivity, not measured bond angles. Compare the molecular formula with the arrangement of atoms.
Explore: Move a branch or functional group and check how the numbering and name change.
Name CH3CH(CH3)CH2CH2OH, identify its alcohol class and explain how the parent chain and numbering are chosen.
- Choose the four-carbon chain containing the carbon bearing OH. [1 mark]
- Number from the OH end, placing it at carbon 1. [1 mark]
- The methyl substituent is at carbon 3: 3-methylbutan-1-ol. [1 mark]
- The OH-bearing carbon bonds to only one other carbon, so the alcohol is primary. [1 mark]
Answer: 3-methylbutan-1-ol, primary alcohol.
Assumed knowledge
A displayed or condensed structure can be traced carbon by carbon.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Name chains up to ten carbons with simple branches.
- Assign functional-group and substituent positions.
- Classify alcohol and haloalkane carbons.