Arrange the following alcohols in decreasing order of acidity:
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (D), (A), (C), (B)
Reasoning:
Acidity of alcohols depends on the stability of the alkoxide ion formed after loss of H⁺. Alkyl groups show a +I (electron-donating) effect, which destabilizes the negative charge on oxygen and reduces acidity.
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D (methanol) has no electron-donating alkyl groups → most acidic.
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A (ethanol) has one alkyl group → acidity decreases slightly.
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C (isopropanol) has two alkyl groups → acidity decreases further.
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B (tert-butanol) has three alkyl groups → strongest +I effect → least acidic.
Hence, acidity decreases in the order: methanol > ethanol > isopropanol > tert-butanol.
Decreasing order of acidity:
$\text{D (CH₃OH)} > \text{A (CH₃CH₂OH)} > \text{C ((CH₃)₂CH–OH)} > \text{B ((CH₃)₃C–OH)}$