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Basics of Organic Chemistry question

2017 · Shift 1 · Q11
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Basics of Organic Chemistry question

2017 · Shift 1 · Q11

JEE AdvancedChemistryBasics of Organic ChemistryMultiple correct+4 / −1
The correct statements(s) for the following addition reactions is (are) JEE Advanced 2017 Paper 1 Offline Chemistry - Basics of Organic Chemistry Question 38 English
  1. A
    OOO and PPP are identical molecules
  2. B
    (MMM and OOO) and (NNN and PPP) are two pairs of diastereomers
  3. C
    (MMM and OOO) and (NNN and PPP) are two pairs of enantiomers
  4. D
    Bromination proceeds through trans-addition in both the reactions
View written solutionFree

Correct answer: B, D

  1. Interpret the question

    The question refers to bromine addition reactions giving products M,N,O,PM, N, O, PM,N,O,P, and asks which stereochemical statements are correct.

    For alkene bromination:

    • reaction proceeds via a bromonium ion intermediate,
    • nucleophilic attack of Br−Br^-Br− occurs from the opposite side,
    • hence the addition is anti (or trans-addition across the double bond framework).

    Therefore, statement D is expected to be correct if both reactions are ordinary brominations of alkenes.

  1. General stereochemical outcome of bromination

    For an alkene with two different substituents on the double-bond carbons, anti addition of bromine creates two stereocentres.

    • Starting from one alkene geometry, one enantiomeric/diastereomeric set is formed.
    • Starting from the other alkene geometry, a different stereochemical set is formed.

    Importantly:

    • cis and trans alkenes do not generally give the same dibromide,
    • instead they give different stereoisomeric products, typically related as diastereomers.

  1. Check option A: OOO and PPP are identical molecules

    Since the two reactions correspond to different stereochemical starting situations, the anti addition products are not identical in general.

    Thus, OOO and PPP are not identical.

    So, A is false.

  1. Check options B and C

    The products from bromination of one alkene geometry form one stereochemical pair, and products from the other alkene geometry form another pair.

    Comparing across the two sets:

    • (M,O)(M, O)(M,O) are related as diastereomers,
    • (N,P)(N, P)(N,P) are related as diastereomers.

    They are not enantiomer pairs.

    Hence:

    • B is true,
    • C is false.

  1. Check option D

    As discussed, bromination of alkenes proceeds through a cyclic bromonium ion and gives anti/trans addition in both reactions.

    So, D is true.

  1. Final result

    Correct statements are: B,D\boxed{B, D}B,D​

  1. Comparison with stored answer

    Stored correct answer: B, D

    Our derived answer matches the stored answer exactly.

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