How to Write IUPAC Names?
IUPAC (International Union of Pure and Applied Chemistry) provides a systematic way to name organic compounds. By following specific rules, we can determine the correct name for any organic molecule.
Steps to Write the IUPAC Name:
1. Identify the Longest Carbon Chain (Parent Chain)
- Select the longest continuous carbon chain that includes the most functional groups, double/triple bonds, and substituents.
- The name of this chain is based on alkane, alkene, or alkyne structures.
2. Identify the Functional Group
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The principal functional group determines the suffix of the compound’s name.
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The following table lists common functional groups and their suffixes:
3. Number the Parent Chain
- Number the carbon chain from the end closest to the principal functional group to assign the lowest possible number to it.
- If there is no functional group, prioritize numbering based on double/triple bonds or substituents.
4. Identify and Name the Substituents
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Any groups attached to the main chain (like –CH₃, –Cl, –Br, –NO₂) are named as prefixes.
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Their position on the chain must be indicated with numbers.
Common Substituents and Prefixes:
5. Write the Name in the Correct Order
The final IUPAC name follows this order:
(Position Number + Prefix + Parent Chain Name + Suffix)
If multiple identical substituents are present, use di-, tri-, tetra- as prefixes.
Substituents are arranged alphabetically, ignoring prefixes like di-, tri-, etc.
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Examples of IUPAC Naming
1. CH₃-CH₂-CH₂-CH₃
Longest chain: 4 carbons → Butane
No functional group → Final Name: Butane
2. CH₃-CH(OH)-CH₃
Longest chain: 3 carbons → Propane
Functional group: -OH (Alcohol) → Use -ol
Positioning: Give -OH the lowest number → Final Name: Propan-2-ol
3. CH₃-CH₂-CH=CH₂
Longest chain: 4 carbons → Butene
Double bond is at position 1 → Final Name: But-1-ene
4. CH₃-CHCl-CH₂-CH₃
Longest chain: 4 carbons → Butane
Substituent: Chloro (-Cl)
Positioning: Assign Cl the lowest number → Final Name: 2-Chlorobutane
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Conclusion
✔ Identify the longest carbon chain.
✔ Find the principal functional group and assign it a suffix.
✔ Number the chain to give the lowest possible numbers.
✔ Identify and name substituents with position numbers.
✔ Arrange names in the correct IUPAC order.
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