Sample 1Medium
Four structural formulas are drawn side by side, each a –COOH group attached to a carbon: in I the carbon is CH2F, in II it is CH2Cl, in III it is CH2Br, and in IV it is CH3. What is the order of their acid strength?
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The answer is A.
An electron-withdrawing halogen stabilises the carboxylate ion by its –I effect, and this effect is strongest for the most electronegative halogen. So FCH2COOH > ClCH2COOH > BrCH2COOH > CH3COOH.
- B.
This is the reverse order; electron-withdrawing halogens increase acidity and CH3 decreases it.
- C.
The –I effect of the halogen follows electronegativity, F > Cl > Br, not atomic size.
- D.
CH3COOH is the weakest, since the methyl group has no electron-withdrawing effect.
NCERT: Class 12 Chemistry, Chapter 8