The correct IUPAC name of the given compound is:

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Accepted Answer

1. **Structure Deduction:** The options describe a hydrocarbon with a double bond. Comparing Options 3 and 4 suggests the structure involves a 6-carbon chain containing a double bond, with ethyl and propyl groups attached. The probable structure is $CH_2=CH-CH(CH_2CH_2CH_3)-CH(CH_2CH_3)-CH_2CH_3$.
2. **Longest Chain Selection:**
   - The parent chain must contain the double bond ($C=C$).
   - There are two possible 6-carbon chains containing the double bond:
     - Path A (Straight): $C_1-C_2-C_3-C_4-C_5-C_6$. This chain has **two substituents**: a propyl group at C-3 and an ethyl group at C-4.
     - Path B (Turning into the propyl group): $C_1-C_2-C_3-C(Pr)$. This chain also has 6 carbons but results in only **one complex substituent** (1-ethylpropyl) at C-3.
   - **Rule:** If two chains have the same length, the one with the **greater number of substituents** is chosen as the parent chain [NCERT 11th, Ch 12, Sec 12.5.2; Source 83, 84]. Thus, Path A is selected.
3. **Numbering:** Numbering starts from the end giving the double bond the lowest locant. $C_1$ is the double-bonded carbon ($=CH_2$). This makes the double bond position 1.
4. **Naming:** Substituents are listed alphabetically: **E**thyl before **P**ropyl.
   - Position 4: Ethyl
   - Position 3: Propyl
   - Parent: Hex-1-ene
   - Full Name: **4-Ethyl-3-propylhex-1-ene**.
5. **Analysis of Other Options:**
   - Option 2 is incorrect because numbering must give the double bond the lowest number (1-ene, not 5-ene).
   - Option 3 is incorrect because it chooses the chain with fewer substituents.

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