IUPAC Naming: Root, Suffix and Prefix
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How a chemical name is built from a molecule: the root counts the parent chain's carbons, the suffix gives its bonds and principal group, and the prefix names what is attached.
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Key points
- Root: the number of carbons in the parent chain: meth 1, eth 2, prop 3, but 4, pent 5, hex 6.
- Primary suffix: the bonds in the chain: -ane (all single), -ene (C=C), -yne (C≡C).
- Secondary suffix: the principal functional group: -ol (–OH), -al (–CHO), -one (C=O inside the chain), -oic acid (–COOH).
- Prefix: groups attached to the parent chain: methyl (CH₃–), ethyl (C₂H₅–), chloro (Cl–), bromo (Br–), nitro (NO₂–).
- Number the chain so the principal group gets the lowest locant: CH₃–CH(CH₃)–CH₂OH is 2-methylpropan-1-ol.
The parts of a name
| Part | Tells you | Examples |
|---|---|---|
| Prefix | what is attached, and where | 2-methyl, 2-chloro |
| Root | carbons in the parent chain | meth, eth, prop, but, pent, hex |
| Primary suffix | single, double or triple C–C bonds | -ane / -an, -ene, -yne |
| Secondary suffix | the principal functional group | -ol, -al, -one, -oic acid |
The final "e" of -ane is dropped before a suffix that starts with a vowel: propane → propan-1-ol, propanal, propanone.
Worked example: 2-methylpropan-1-ol
CH₃–CH(CH₃)–CH₂OH. The longest chain that contains the –OH has 3 carbons → prop. All bonds are single → an. The –OH is the principal group → ol. Numbering from the –OH end puts it on C1 → propan-1-ol. A CH₃ branch sits on C2 → 2-methyl. Name: 2-methylpropan-1-ol.
| Molecule | Name |
|---|---|
| CH₃CH₂CH₂CH₃ | butane |
| CH₂=CHCH₃ | propene |
| CH₃CH₂OH | ethanol |
| CH₃CH(OH)CH₃ | propan-2-ol |
| CH₃CH₂CHO | propanal |
| CH₃COCH₃ | propanone |
| CH₃CHClCH₃ | 2-chloropropane |
| CH₃CH(OH)CH₂CH₃ | butan-2-ol |
This page covers the basic logic. Choosing the parent chain when several groups compete, functional-group priority, alphabetical order of prefixes and multiple substituents come next in the series.
Try it yourself
Goal: Build the IUPAC name of each molecule from its root, bonds, suffix, prefix and numbering direction, and see which part decides each piece of the name.
- Count the carbons in the parent chain and pick the root.
- Pick the bonds in the chain (an, en or yn).
- Pick the principal group (the suffix) and any attached group (the prefix).
- Choose which end to number from.
- Check your name, then try the next molecule.
Quick quiz
5 questions. Choose an answer for each, then submit to see your score and the explanations.
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