JEE Main · 2019 · Shift-IIeasyHALO-113

The major product of the following reaction is:

Haloalkanes & Haloarenes · Class 12 · JEE Main Previous Year Question

Question

The major product of the following reaction is: image

Options
  1. a

    image

  2. b

    image

  3. c

    image

  4. d

    image

Correct Answerd

image

Detailed Solution

Step 1: First reaction - Free radical chlorination

Toluene + \ceCl2\ce{Cl2}/light:

Free radical substitution at benzylic position (most reactive)

\ceC6H5CH3+Cl2>[hv]C6H5CH2Cl+HCl\ce{C6H5-CH3 + Cl2 ->[hv] C6H5-CH2Cl + HCl}

Product: Benzyl chloride

Step 2: Second reaction - Hydrolysis

Benzyl chloride + \ceH2O\ce{H2O}/heat:

SNS_N substitution (benzylic position is very reactive)

\ceC6H5CH2Cl+H2O>[Δ]C6H5CH2OH+HCl\ce{C6H5-CH2Cl + H2O ->[Δ] C6H5-CH2OH + HCl}

Product: Benzyl alcohol

Answer: (a) Benzyl alcohol (\ceC6H5CH2OH\ce{C6H5CH2OH})

Key Reactions:

Free radical halogenation:

  • Requires light or heat
  • Selectivity: Benzylic > Allylic > 3° > 2° > 1°
  • Benzylic C-H bonds are weakest (most reactive)

Benzylic reactivity:

  • Benzylic radicals are stabilized by resonance
  • Benzylic carbocations are stabilized by resonance
  • Both SN1S_N1 and SN2S_N2 are fast at benzylic position

Common mistake:

  • Thinking Cl₂/light will chlorinate the ring (that needs Lewis acid)
  • Free radical conditions favor side-chain substitution

Alternative products with excess Cl₂:

  • \ceC6H5CHCl2\ce{C6H5-CHCl2} (benzal chloride)
  • \ceC6H5CCl3\ce{C6H5-CCl3} (benzotrichloride)

But with 1 equiv Cl₂, benzyl chloride is major product.

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