The correct order of decreasing acidity of the following aliphatic acids is
(1) HCOOH (CH3)3CCOOH

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Question

The correct order of decreasing acidity of the following aliphatic acids is
(1) HCOOH > (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH
(2) (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH > HCOOH
(3) CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH > HCOOH
(4) HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH

Accepted Answer

Correct Answer: D — HCOOH > CH₃COOH > (CH₃)₂CHCOOH > (CH₃)₃CCOOHStep-by-step Solution:Acidity of carboxylic acids depends on stability of the carboxylate anion (RCOO⁻). Alkyl groups are electron-donating (+I effect), which destabilises RCOO⁻ → decreases acidity. More alkyl groups = greater +I effect = lower acidity.HCOOH: No alkyl group → most stable HCOO⁻ → highest acidity (Ka ≈ 1.77×10⁻⁴)CH₃COOH: One methyl (–CH₃) → moderate +I → Ka ≈ 1.8×10⁻⁵(CH₃)₂CHCOOH: Isopropyl group (two CH₃ on α-C) → stronger +I → less acidic(CH₃)₃CCOOH: tert-Butyl group (three CH₃) → maximum +I → lowest acidityOrder: HCOOH > CH₃COOH > (CH₃)₂CHCOOH > (CH₃)₃CCOOHWhy other options are wrong: B reverses the order entirely; A and C have wrong intermediate positions.Key Concepts:+I effect of alkyl groups: Electron-donating → destabilises carboxylate anion → decreases acidity.Acidity ∝ stability of conjugate base (RCOO⁻).Electron-withdrawing groups (−I effect, e.g., –Cl, –F) increase acidity; electron-donating groups (+I, alkyl) decrease acidity.

The correct order of decreasing acidity of the following aliphatic acids is (1) HCOOH > (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH (2) (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH > HCOOH (3) CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH > HCOOH (4) HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH

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The correct order of decreasing acidity of the following aliphatic acids is (1) HCOOH > (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH (2) (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH > HCOOH (3) CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH > HCOOH (4) HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH

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