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Hydrocarbons question

2019 · 12 Apr · Shift 1 · Q11
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Hydrocarbons question

2019 · 12 Apr · Shift 1 · Q11

JEE MainChemistryHydrocarbonsMCQ+4 / −1
The major product of the following addition reaction is : H3CH_3CH3​C–CHCHCH=CH2CH_2CH2​ →Cl2/H2O\xrightarrow{C{l_2}/{H_2}O}Cl2​/H2​O​
  1. A
    JEE Main 2019 (Online) 12th April Morning Slot Chemistry - Hydrocarbons Question 110 English Option 1
  2. B
    JEE Main 2019 (Online) 12th April Morning Slot Chemistry - Hydrocarbons Question 110 English Option 2
  3. C
    JEE Main 2019 (Online) 12th April Morning Slot Chemistry - Hydrocarbons Question 110 English Option 3
  4. D
    JEE Main 2019 (Online) 12th April Morning Slot Chemistry - Hydrocarbons Question 110 English Option 4
View written solutionFree

Correct answer: B

  1. Identify the reaction type

The alkene is propene:

CH3−CH=CH2CH_3-CH=CH_2CH3​−CH=CH2​

Reaction with Cl2/H2OCl_2/H_2OCl2​/H2​O gives a halohydrin formation reaction.

In water, Cl2Cl_2Cl2​ forms:

Cl2+H2O⇌HOCl+HClCl_2 + H_2O \rightleftharpoons HOCl + HClCl2​+H2​O⇌HOCl+HCl

So effectively, the alkene adds OH and Cl across the double bond.


  1. Mechanism concept

The alkene first forms a chloronium ion intermediate. Then water attacks the more substituted carbon because it bears greater partial positive character.

For propene:

CH3−CH=CH2CH_3-CH=CH_2CH3​−CH=CH2​

  • Middle carbon is more substituted.
  • Terminal carbon is less substituted.

Hence:

  • OHOHOH goes to the more substituted carbon.
  • ClClCl goes to the less substituted carbon.

  1. Write the product

Adding OHOHOH to carbon-2 and ClClCl to carbon-3 gives:

CH3−CH(OH)−CH2ClCH_3-CH(OH)-CH_2ClCH3​−CH(OH)−CH2​Cl

This is 1-chloropropan-2-ol.


  1. Major product

Therefore, the major product is:

CH3−CH(OH)−CH2Cl\boxed{CH_3-CH(OH)-CH_2Cl}CH3​−CH(OH)−CH2​Cl​


  1. Comparison with stored answer

The stored correct answer is B. Since the actual structures for options A–D are not shown, I infer that B corresponds to:

CH3−CH(OH)−CH2ClCH_3-CH(OH)-CH_2ClCH3​−CH(OH)−CH2​Cl

So I agree with the stored answer, provided option B is this halohydrin product.

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