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Haloalkanes and Haloarenes question

2025 · 4 Apr · Shift 2 · Q18
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Haloalkanes and Haloarenes question

2025 · 4 Apr · Shift 2 · Q18

JEE MainChemistryHaloalkanes and HaloarenesMCQ+4 / −1
Given below are two statements : Statement (I) : Alcohols are formed when alkyl chlorides are treated with aqueous potassium hydroxide by elimination reaction. Statement (II) : In alcoholic potassium hydroxide, alkyl chlorides form alkenes by abstracting the hydrogen from the β\betaβ-carbon. In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Both Statement I and Statement II are incorrect
  2. B
    Both Statement I and Statement II are correct
  3. C
    Statement I is incorrect but Statement II is correct
  4. D
    Statement I is correct but Statement II is incorrect
View written solutionFree

Correct answer: C

  1. Analyze Statement (I)

    Statement (I): Alcohols are formed when alkyl chlorides are treated with aqueous potassium hydroxide by elimination reaction.

    • When an alkyl chloride reacts with aqueous KOH, the major reaction is nucleophilic substitution, not elimination.
    • The hydroxide ion (OH−)\left(\mathrm{OH^-}\right)(OH−) replaces the chloride ion: R−Cl+KOH(aq)→R−OH+KCl\mathrm{R-Cl + KOH(aq) \rightarrow R-OH + KCl}R−Cl+KOH(aq)→R−OH+KCl
    • Thus, alcohol is indeed formed, but by substitution reaction, not by elimination.

    Therefore, Statement (I) is incorrect.

  2. Analyze Statement (II)

    Statement (II): In alcoholic potassium hydroxide, alkyl chlorides form alkenes by abstracting the hydrogen from the β\betaβ-carbon.

    • In alcoholic KOH, elimination is favored.
    • The base removes a hydrogen from the β\betaβ-carbon, and the halogen leaves from the adjacent carbon, leading to formation of a double bond: R−CH2−CH2−Cl→alc. KOHR−CH=CH2+KCl+H2O\mathrm{R-CH_2-CH_2-Cl \xrightarrow[alc.\ KOH]{} R-CH=CH_2 + KCl + H_2O}R−CH2​−CH2​−Clalc. KOH​R−CH=CH2​+KCl+H2​O
    • This is β\betaβ-elimination (dehydrohalogenation).

    Therefore, Statement (II) is correct.

  3. Evaluate the options

    • A: Both incorrect →\rightarrow→ False
    • B: Both correct →\rightarrow→ False
    • C: Statement I incorrect but Statement II correct →\rightarrow→ True
    • D: Statement I correct but Statement II incorrect →\rightarrow→ False
  4. Final Answer

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

  5. Comparison with stored answer

    • Derived answer: C
    • Stored correct answer: C
    • They match.
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