4CH1
Introduction to Organic Chemistry
Organic Chemistry · 2 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 3% of your exam marks.
stable
Rare
Stable3%
Homologous series, IUPAC naming and functional groups; often a short opening question.
Two-part naming convention
- An organic compound's name has two parts: a stem (or prefix) and an ending (or suffix)
- The stem records the length of the longest continuous chain — how many carbons are joined end to end
- The ending tells you which functional group the molecule contains
Stems for the first six carbon-chain lengths
| Number of C atoms | Stem |
|---|---|
| 1 | meth- |
| 2 | eth- |
| 3 | prop- |
| 4 | but- |
| 5 | pent- |
| 6 | hex- |
- These six are the only stems you need to recognise
Endings for each homologous series
| Ending | Functional group it represents | Homologous series |
|---|---|---|
| -ane | (no functional group; all single bonds) | Alkanes |
| -ene | C=C double bond | Alkenes |
| -anol | –OH attached to a carbon | Alcohols |
| -anoic acid | –COOH (carboxyl group) | Carboxylic acids |
| -yl …anoate | –COO– (ester linkage) | Esters |
| -amine | –NH2 | Amines |
Building a name from its stem and ending
- Two-carbon chain with all single bonds: eth-ane → ethane
- Two-carbon chain with a C=C: eth-ene → ethene
- Three-carbon chain with an –OH: prop-anol → propanol
- Four-carbon chain with a –COOH: but-anoic acid → butanoic acid
Numbering a functional group's position
- When a chain has more than two carbons, the functional group can sit on different carbons; numbering shows which
- Number the carbons starting from the end nearest the functional group
- Insert the number between the stem and the ending, separated by hyphens
- Example: propan-1-ol has the –OH on the first carbon (CH3CH2CH2OH); propan-2-ol has the –OH on the middle carbon (CH3CH(OH)CH3)
- Numbered names are usually needed only for alcohols and alkenes where the choice of carbon matters
Naming polysubstituted molecules
- For two of the same functional group, attach a di- prefix to the ending and list the two carbon numbers separated by a comma
- Example: ethane-1,2-diol (the antifreeze used in car radiators) has an –OH on each of its two carbons (HOCH2CH2OH)