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NEET CHEMISTRYMedium

The correct IUPAC name of the given compound is:

A

3-Ethyl-4-ethenylheptane

B

3-Ethyl-4-propylhex-5-ene

C

3-(1-Ethyl propyl) hex-1-ene

D

4-Ethyl-3-propylhex-1-ene

Step-by-Step Solution

  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 CH2=CH−CH(CH2CH2CH3)−CH(CH2CH3)−CH2CH3CH_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=CC=C).
  • There are two possible 6-carbon chains containing the double bond:
  • Path A (Straight): C1−C2−C3−C4−C5−C6C_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): C1−C2−C3−C(Pr)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.
  1. Numbering: Numbering starts from the end giving the double bond the lowest locant. C1C_1 is the double-bonded carbon (=CH2=CH_2). This makes the double bond position 1.
  2. Naming: Substituents are listed alphabetically: Ethyl before Propyl.
  • Position 4: Ethyl
  • Position 3: Propyl
  • Parent: Hex-1-ene
  • Full Name: 4-Ethyl-3-propylhex-1-ene.
  1. 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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