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JEE Main 2020 · Chemistry · Hydrocarbons · medium

A hydrocarbon on reductive ozonolysis (O3, then Zn/H2O) gives only propanone and propanal. The major product when this hydrocarbon reacts with HBr…

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A hydrocarbon on reductive ozonolysis (O3\mathrm{O_3}, then Zn/H2O\mathrm{Zn/H_2O}) gives only propanone and propanal. The major product when this hydrocarbon reacts with HBr (no peroxide) is
  1. A. 2-bromo-2-methylpentane
  2. B. 3-bromo-2-methylpentane
  3. C. 2-bromo-4-methylpentane
  4. D. 1-bromo-2-methylpentane
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Answer: (A) 2-bromo-2-methylpentane

Joining the carbonyl carbons gives (CH3)2C=CH−CH2CH3\mathrm{(CH_3)_2C=CH-CH_2CH_3} (2-methylpent-2-ene). Markovnikov addition places H+\mathrm{H^+} on the less substituted carbon, forming the tertiary carbocation at C2\mathrm{C_2}, which is attacked by Br−\mathrm{Br^-}: (CH3)2CBr−CH2CH2CH3\mathrm{(CH_3)_2CBr-CH_2CH_2CH_3}, i.e. 2-bromo-2-methylpentane.
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