📋 The IUPAC Algorithm
- Find the longest continuous carbon chain containing the highest-priority functional group → root name (meth-, eth-, prop-, but-, pent-, hex-...)
- Number the chain so the principal functional group gets the lowest possible locant
- Add the suffix for the principal group (-ol, -al, -one, -oic acid, -amine, -amide)
- Name substituents as prefixes (methyl-, ethyl-, chloro-, hydroxy-) with locants
- List prefixes alphabetically. Ignore di-, tri-, etc. When ordering
Carbon Chain Roots
| C atoms | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Root | meth- | eth- | prop- | but- | pent- | hex- | hept- | oct- |
⚠️ Common Examiner Traps
- Hidden longest chains. The chain may bend at 90° in the drawing; it's still continuous!
- Impossible names. "4-methylpentane" is wrong; numbering from the other end gives 2-methylpentane
- Redundant locants. Don't write "1-ethanol" or "ethan-1-ol" when the -OH can only be at position 1 (use "ethanol" instead)
- Terminal groups are always C-1. Aldehydes (-CHO) and carboxylic acids (-COOH) must be at carbon 1. Write butanal, not butan-1-al; write propanoic acid, not propan-1-oic acid
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