IUPAC Rules and Nomenclature – Full Explanation

IUPAC Rules and Nomenclature in Organic Chemistry

IUPAC (International Union of Pure and Applied Chemistry) provides a standardized system for naming chemical compounds. It ensures that every compound has a unique, unambiguous name that reflects its structure.

🔹 Importance of IUPAC Nomenclature

• Standardized naming across the world
• Avoids confusion caused by common or trivial names
• Useful in exams like NEET, JEE, CBSE, ICSE

📚 Basic IUPAC Rules for Naming Organic Compounds

1️⃣ Identify the Longest Continuous Carbon Chain

This chain determines the parent name of the compound.

Example: For CH₃-CH₂-CH₂-CH₃, the longest chain is 4 carbons → Butane

2️⃣ Number the Chain from the End Nearest to the Substituent

This ensures that substituents get the lowest possible number.

3️⃣ Identify and Name the Substituents (Alkyl Groups)

• CH₃ → Methyl
• CH₂CH₃ → Ethyl
• Cl → Chloro, Br → Bromo, NO₂ → Nitro

4️⃣ Assign Numbers to Substituents and List Them Alphabetically

If multiple substituents are present, mention their positions and names in alphabetical order (ignoring prefixes like di-, tri-).

5️⃣ Use Prefixes for Identical Substituents

• 2 methyl groups → dimethyl
• 3 ethyl groups → triethyl

6️⃣ Name Functional Groups with Priority

Functional groups have specific suffixes and priority orders. Always give the highest priority group the suffix form and place it at the end of the name.

🔹 Functional Group Priority Order (High → Low)

1. Carboxylic acid (-COOH) → oic acid
2. Acid anhydride
3. Ester (-COOR) → oate
4. Aldehyde (-CHO) → al
5. Ketone (-CO-) → one
6. Alcohol (-OH) → ol
7. Amine (-NH₂) → amine
8. Alkene (-C=C-) → ene
9. Alkyne (-C≡C-) → yne

✅ Example: Naming CH₃-CH(CH₃)-CH₂-OH

1. Longest chain = 3 carbons → propane
2. Substituent = methyl at carbon 2
3. Functional group = OH (alcohol), position 1 → 1-ol
4. Final name = 2-methylpropan-1-ol

🔍 Common Root Names in IUPAC

No. of C Atoms	Root Name
1	Meth
2	Eth
3	Prop
4	But
5	Pent
6	Hex
7	Hept
8	Oct
9	Non
10	Dec

🎯 Tips to Remember

• Always give the lowest number to the highest priority group
• Use hyphens between numbers and words (e.g., 2-methyl)
• Use commas between numbers (e.g., 2,3-dimethyl)
• Alphabetize substituents (not considering di-, tri-)

🧪 Practice Questions

1. Name CH₃-CH₂-CH₂-CH₂-CH₃
2. Name CH₃-CH(CH₃)-CH₂-CH₃
3. Name CH₃-CH₂-CH=CH₂

📌 Internal Links

• Periodic Table – Full Explained
• Reaction Mechanism

Author: Chemistry of Science

Tags: IUPAC Rules, Organic Chemistry, NEET Chemistry, CBSE Class 11, Nomenclature