DAT Review · Organic Chemistry
IUPAC Nomenclature of Organic Compounds
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Scope: IUPAC systematic naming of alkanes, alkenes, alkynes, and compounds with functional groups. You must identify the parent chain, number it correctly, name substituents alphabetically, and apply functional group priority rules. Expect 2–4 questions testing parent chain selection, numbering, stereochemical prefixes, and functional group suffix priority.
The college version
Core Review
Parent Chain Selection
Find the longest continuous chain of carbon atoms. If two chains of equal length exist, choose the one with more substituents (more branching). The parent name suffix depends on saturation: alkanes (-ane), alkenes (-ene), alkynes (-yne). For cyclic compounds, prefix with "cyclo-".
Numbering the Chain
Number from the end that gives the highest-priority functional group the lowest number. If no functional group is present, number to give the first substituent (or first point of difference) the lowest number. For alkenes and alkynes, the multiple bond takes priority over alkyl substituents in numbering.
Substituent Naming
Alkyl substituents: methyl (-CH₃), ethyl (-CH₂CH₃), propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl. Halogen substituents: fluoro-, chloro-, bromo-, iodo-. List substituents alphabetically (ignore prefixes like di-, tri-, sec-, tert-; but do NOT ignore iso- or cyclo-). Use di-, tri-, tetra- for multiple identical substituents.
Functional Group Priority (Highest to Lowest)
| Priority | Functional Group | Suffix (if highest) | Prefix (if lower) |
|---|---|---|---|
| 1 | Carboxylic acid | -oic acid | carboxy- |
| 2 | Ester | -oate | alkoxycarbonyl- |
| 3 | Amide | -amide | carbamoyl- |
| 4 | Nitrile | -nitrile | cyano- |
| 5 | Aldehyde | -al | formyl- (or oxo-) |
| 6 | Ketone | -one | oxo- |
| 7 | Alcohol | -ol | hydroxy- |
| 8 | Amine | -amine | amino- |
| 9 | Alkene | -ene | alkenyl- |
| 10 | Alkyne | -yne | alkynyl- |
| 11 | Alkane | -ane | alkyl- |
The highest-priority group determines the suffix; all lower-priority groups become prefixes.
Alkenes and Alkynes
For alkenes, the double bond gets the lowest number. Specify configuration using (E)/(Z) — Z when higher-priority groups are on the same side, E when on opposite sides (from German zusammen = together, entgegen = opposite). Multiple double/triple bonds use -diene, -triene, -diyne, etc. The parent name includes the position of each multiple bond: buta-1,3-diene.
Cyclic Compounds
Number the ring starting at a substituent, proceeding in the direction that gives the lowest numbers to other substituents. If a ring contains a functional group, that carbon gets position 1.
Alcohols, Ethers, and Amines
- Alcohols: suffix -ol. Number to give the OH the lowest number (e.g., propan-2-ol).
- Ethers: named as alkoxyalkanes (e.g., methoxyethane).
- Amines: suffix -amine or prefix amino-. For secondary/tertiary amines, use N-alkyl prefixes (e.g., N-methylethanamine).
Carbonyl Compounds
- Aldehydes: suffix -al. The aldehyde carbon is always C-1 (no locant needed for linear aldehydes).
- Ketones: suffix -one. Number to give the carbonyl the lowest number (e.g., pentan-2-one).
- Carboxylic acids: suffix -oic acid. The carboxyl carbon is always C-1.
- Esters: named as alkyl alkanoates (alkyl from alcohol portion, alkanoate from acid portion).
- Amides: suffix -amide. N-substituted amides use N-alkyl prefix.
Common Traps
- Longest chain ≠ parent chain: A shorter chain containing the functional group wins.
- Alphabetical vs. numerical: Substituents are ordered alphabetically in the name, but numbered from whichever end gives the lowest locants. These are independent rules.
- sec- and tert- are ignored in alphabetization; iso- and neo- are NOT ignored.
- Forgetting stereochemistry: If E/Z or R/S is specified, include it at the front of the name.
- Esters are backwards: The alcohol-derived alkyl group comes first, then the acid-derived alkanoate.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Imagine naming a person: last name (parent chain), first name (substituents), and house number (locants). The "most important" part of the molecule gets to be the last name (suffix). Everything else is a "first name" (prefix) listed alphabetically. Numbering tells you exactly where each piece lives on the carbon chain.
Key takeaways
- Parent chain MUST include the highest-priority functional group even if a longer carbon chain exists without it.
- Numbering tiebreakers: Functional group > multiple bond > first substituent > alphabetically first substituent.
- Alphabetical ordering ignores multiplicative prefixes (di-, tri-, tetra-) but NOT iso-, cyclo-, neo-.
- Carboxylic acids, esters, and amides always have their carbonyl carbon as C-1 (no number needed).
- Common trivial names tested: acetone (propanone), formaldehyde (methanal), acetic acid (ethanoic acid), ethylene (ethene), acetylene (ethyne).
- Name: CH₃CH₂CH(CH₃)CH₂COOH. Answer: 3-methylpentanoic acid. The longest chain containing COOH is 5 carbons (pentanoic acid). Numbering from COOH (C-1), the methyl is at C-3.
- Which has higher priority: an aldehyde or a ketone? Answer: Aldehyde (-al) outranks ketone (-one). A molecule with both would be named as an aldehyde with the ketone as an "oxo-" prefix.
- Name: (CH₃)₂CHCH₂CH(OH)CH₃. Answer: 4-methylpentan-2-ol. The 5-carbon chain gives pentane; OH gets lowest number (C-2), methyl substituent at C-4.
Study tools & related lessonsYou’ll learn to · Related
You’ll learn to
- Select the longest continuous carbon chain as the parent name
- Number the chain to give the highest-priority functional group the lowest possible number
- Name substituents alphabetically with appropriate locants
- Apply the IUPAC functional group priority order correctly
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