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MCQEasyJEE 2024Phenols

JEE Chemistry 2024 Question with Solution

Among the following, the most acidic compound is:

  • A

    Benzene

  • B

    Phenol

  • C

    Ethanol

  • D

    Acetylene

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: The compounds are Benzene, Phenol, Ethanol, and Acetylene.

Find: Which compound is the most acidic.

The solution discusses a different question about electrophilic aromatic substitution and reactivity order, so it cannot be used to derive the answer for this acidity question. Therefore, we use the listed correct answer field here.

Among the given compounds, Phenol is the most acidic because the conjugate base of phenol, phenoxide ion, is stabilized by resonance over the aromatic ring. Benzene is very weakly acidic, ethanol is less acidic than phenol, and acetylene, although acidic relative to many hydrocarbons, is still less acidic than phenol.

Therefore, the correct option is B.

Common mistakes

  • Comparing only the presence of hydrogen without considering conjugate base stability is incorrect. Acidity depends on the stability of the conjugate base. Always compare the stabilization after proton loss.

  • Assuming ethanol is more acidic than phenol because both contain an −OH-OH group is incorrect. The phenoxide ion is resonance-stabilized, while ethoxide ion is not. Always check resonance effects.

  • Thinking acetylene is the most acidic just because it is an unsaturated compound is incorrect. Its conjugate base has greater ss-character than alkane carbanions, but phenol remains more acidic here. Compare actual relative acid strengths.

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