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Basics of Organic Chemistry question

2021 · 31 Aug · Shift 1 · Q10
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Basics of Organic Chemistry question

2021 · 31 Aug · Shift 1 · Q10

JEE MainChemistryBasics of Organic ChemistryMCQ+4 / −1
Choose the correct name for compound given below : JEE Main 2021 (Online) 31st August Morning Shift Chemistry - Basics of Organic Chemistry Question 149 English
  1. A
    (4E)-5-Bromo-hex-4-en-2-yne
  2. B
    (2E)-2-Bromo-hex-4-yn-2-ene
  3. C
    (2E)-2-Bromo-hex-2-en-4-yne
  4. D
    (4E)-5-Bromo-hex-2-en-4-yne
View written solutionFree

Correct answer: C

  1. Identify the parent chain

    The structure corresponds to a six-carbon chain containing both a double bond and a triple bond, so the parent hydrocarbon is hex-en-yne.

  2. Number the chain to give lowest locants to multiple bonds

    For compounds containing both C=CC=CC=C and C≡CC\equiv CC≡C, numbering is chosen so that the set of locants for multiple bonds is lowest.

    Possible numbering gives:

    • From one end: double bond at 222, triple bond at 444
    • From the other end: double bond at 444, triple bond at 222

    Since in a tie the double bond gets the lower number, we choose: hex-2-en-4-yne\text{hex-2-en-4-yne}hex-2-en-4-yne

  3. Locate the substituent

    With this numbering, the bromo substituent is on carbon 222.

    So the name becomes: 2-Bromo-hex-2-en-4-yne2\text{-Bromo-hex-2-en-4-yne}2-Bromo-hex-2-en-4-yne

  4. Assign stereochemistry of the double bond

    At the double bond, assign CIP priorities:

    • On one carbon, BrBrBr has higher priority than CH3CH_3CH3​ / H-type substituent.
    • On the other carbon, the carbon chain has higher priority than H.

    The higher-priority groups are on opposite sides of the double bond, so configuration is E.

    Hence the full name is: (2E)-2-Bromo-hex-2-en-4-yne\boxed{(2E)\text{-2-Bromo-hex-2-en-4-yne}}(2E)-2-Bromo-hex-2-en-4-yne​

  5. Check options

    • A: (4E)(4E)(4E)-5-Bromo-hex-4-en-2-yne ❌
      • Multiple bonds not numbered correctly.
    • B: (2E)(2E)(2E)-2-Bromo-hex-4-yn-2-ene ❌
      • Although similar in meaning, IUPAC format prefers en before yne in the suffix pattern as hex-2-en-4-yne.
    • C: (2E)(2E)(2E)-2-Bromo-hex-2-en-4-yne ✅
    • D: (4E)(4E)(4E)-5-Bromo-hex-2-en-4-yne ❌
      • Wrong substituent position and stereodescriptor numbering.
  6. Final answer

    The correct option is: C\boxed{\text{C}}C​

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