IUPAC Nomenclature – Rules for Selection of Parent Chain In easy way Part 03.

IUPAC Nomenclature – Rules for Selection of Parent Chain (Easy Way) | Part 03

When naming organic compounds using IUPAC (International Union of Pure and Applied Chemistry) rules, selecting the longest parent chain is the most crucial step. Here’s how you can do it easily:

 Rule 1: Select the Longest Continuous Chain

 The parent chain is the longest continuous carbon chain present in the compound.

Example:
CH₃–CH₂–CH₂–CH₃ (Butane)
CH₃–CH–CH₂–CH₃
   |
  CH₃
Here, the longest chain has 4 carbon atoms, so the parent name is butane.

 Rule 2: Consider the Chain with Maximum Substituents

 If two chains of equal length exist, choose the one with more branches (substituents).

Example:
CH₃–CH₂–CH–CH₃
   |
  CH₃
(Choose the chain with the methyl (-CH₃) group)

 Rule 3: Consider Functional Groups

 If a functional group (like –OH, –COOH, =O, –NH₂) is present, choose the longest chain that includes the functional group.

Example:
CH₃–CH–CH₂–COOH
   |
  CH₃
(The chain must include -COOH (carboxyl group), so the parent chain is butanoic acid).

 Rule 4: Priority Order for Functional Groups

 If multiple functional groups are present, follow this priority order for selecting the chain:
-COOH (Carboxylic acid) > -SO₃H (Sulfonic acid) > -COO- (Ester) > -CHO (Aldehyde) > -C=O (Ketone) > -OH (Alcohol) > -NH₂ (Amine) > Alkene > Alkyne > Alkane

Example:
CH₃–CH₂–CH–OH
   |
  CH₃
(Here, the chain must include -OH, so it is butanol).

 Rule 5: Choose the Chain with Maximum Double or Triple Bonds

 If alkenes (-C=C-) or alkynes (-C≡C-) are present, the parent chain must include the longest sequence of multiple bonds.

Example:
CH₃–CH=CH–CH₃ (But-2-ene)
(Chain must include the double bond)

 Summary: Easy Way to Select the Parent Chain

Longest chain is the parent chain.
More branches (substituents)? Choose that chain.
Functional groups? Always include them.
Double/triple bonds? Always include them.
If tie? Follow functional group priority.

 Do you want practice questions or more examples?

IUPAC Nomenclature – Rules for Selection of Parent Chain In easy way Part 03.

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Organic Compounds: Alkanes and Cycloalkanes

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Sure! Here’s an easy-to-understand guide to IUPAC Nomenclature – Rules for Selection of Parent Chain (Part-03), simplified for beginners, especially students of Class 11, NEET, JEE, or B.Sc. level.

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IUPAC Nomenclature – Part 03

Rules for Selection of Parent Chain

(In the easiest possible way)

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What is a Parent Chain?

Parent Chain = The longest continuous chain of carbon atoms that contains the principal functional group, multiple bonds, and maximum substituents.

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Basic Rules to Select the Parent Chain (in order of priority):

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Rule 1: Longest Chain Rule

Choose the longest continuous chain of carbon atoms.

Example:
In CH₃–CH₂–CH₂–CH₃
→ Longest chain = 4 carbon atoms → Butane

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Rule 2: Highest Priority Functional Group First

If there’s a functional group (like –OH, –COOH, –CHO, –NH₂), the parent chain must include it, even if it’s not the longest chain.

Example:
CH₃–CH(OH)–CH₂–CH₂–CH₃
→ Include –OH group → Parent chain = 5 carbons
→ Compound = Pentanol

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Rule 3: Maximum Number of Multiple Bonds

If there’s a double (=) or triple (≡) bond, the parent chain should include the maximum number of multiple bonds.

Example:
CH₂=CH–CH₂–C≡CH
→ Include both = and ≡ → Parent chain = 5 carbons
→ Name = Penta-1-en-4-yne

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Rule 4: Maximum Substituents

If there are two or more chains of equal length, choose the one with more substituents.

Example:
Two chains of 6 carbons – one has 2 methyl groups, one has 1
→ Choose the one with 2 methyls (more substituents)

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Rule 5: Lowest Locant Rule

Number the chain so that the functional group, multiple bonds, or substituents get the lowest possible number.

Example:
CH₃–CH₂–CH=CH–CH₃
→ Number from left: But-2-ene, not But-3-ene

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Trick to Remember Order of Priority:

➤ Functional group > Double bond/Triple bond > Substituents

When selecting or numbering, this is the priority order.

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Example Summary:

Molecule	Correct Parent Chain	Reason
CH₃–CH(OH)–CH₂–CH₃	4 carbon chain	Includes –OH (functional group)
CH≡C–CH=CH₂	4 carbon chain	Includes both ≡ and =
CH₃–CH₂–C(CH₃)₂–CH₂–CH₃	5 carbon chain	Has 2 methyl substituents

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Coming Up in Part 04:

• Naming substituents & multiple substituents
• Use of prefixes: di-, tri-, tetra-
• Complex substituents (alkyl branches)

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Would you like:

• A PDF cheat-sheet?
• A video explanation?
• Practice problems with solutions?

Let me know and I’ll send it!

IUPAC Nomenclature – Rules for Selection of Parent Chain In easy way Part 03.