Question 19 of 26intermediate🔍 AnalyzeShort Answer3 marks

Arrange the following compounds in increasing order of their property as indicated: (i) Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN) (ii) CH₃CH₂CH(Br)COOH, CH₃CH(Br)CH₂COOH, (CH₃)₂CHCOOH, CH₃CH₂CH₂COOH (acid strength) (iii) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength)

(i)
Answer

Di-tert-butyl ketone < Methyl tert-butyl ketone < Acetone < Acetaldehyde

(ii)
Answer

(CH₃)₂CHCOOH < CH₃CH₂CH₂COOH < CH₃CH(Br)CH₂COOH < CH₃CH₂CH(Br)COOH

(iii)
Answer

4-Methoxybenzoic acid < Benzoic acid < 4-Nitrobenzoic acid < 3,4-Dinitrobenzoic acid

Explanation

Part (i): HCN addition to carbonyl compounds involves nucleophilic attack. Aldehydes are more reactive than ketones due to less steric hindrance and electronic factors. Among ketones, steric hindrance from bulky groups decreases reactivity. Part (ii): Acid strength increases with electron-withdrawing groups (-I effect) near the carboxylic group. Bromine has a strong electron-withdrawing effect that weakens with distance. Alkyl groups have electron-donating effect (+I effect), decreasing acidity. Part (iii): Electron-withdrawing substituents like -NO₂ increase acidity by stabilizing the carboxylate anion. Electron-donating groups like -OCH₃ decrease acidity. More nitro groups result in stronger acid.

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