IUPAC Rules
The 5-Step IUPAC Systematic Naming Algorithm
- Longest Carbon Chain: Find the longest continuous carbon chain containing the principal functional group (stem: meth-, eth-, prop-, but-, pent-, hex-).
- Principal Suffix: Identify the highest priority functional group to determine the suffix (-oic acid, -al, -one, -ol, -ene, -ane).
- Lowest Locant Rule: Number the chain from the end that gives the principal functional group the lowest number.
- Substituents / Prefixes: Name and number any branching alkyl groups or halogens (e.g. 2-methyl, 3-chloro).
- Alphabetical Assembly: List substituent prefixes alphabetically (di-, tri- prefixes are ignored in alphabetical ordering). Separate numbers with commas and words/numbers with hyphens (e.g.
2,2-dimethylpropan-1-ol).
Carbon Chain Roots
| C atoms | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Root | meth- | eth- | prop- | but- | pent- | hex- | hept- | oct- |
Examiner Trap
Common IUPAC Nomenclature Pitfalls
- Missing Locants: Forgetting locants (e.g. writing "propanol" instead of
propan-1-olorpropan-2-ol). - Bent Chains: Failing to recognise that the longest chain may bend around corners.
- Alphabetical Order: Listing "dimethyl" before "ethyl" (compare "e" of ethyl vs "m" of methyl; ignore "di-").
- Punctuation Errors: Hyphens between numbers and letters (
2-methyl), commas between numbers (2,3-dimethyl).
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