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JEE Main · 2019 · 12 Jan 2019 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

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In the following reaction

Aldehyde + Alcohol Acetal
Aldehyde Alcohol
HCHO BuOH
MeOH
The best combination is
  1. (A) and BuOH
  2. (B)HCHO and MeOH✓ Correct
  3. (C) and MeOH
  4. (D)HCHO and BuOH

Answer: (B)

Solution

Forming an acetal is a nucleophilic addition of the alcohol to the carbonyl, so it runs best when both partners are as unhindered as possible. Among the aldehydes, formaldehyde has only hydrogens around the carbonyl and is the most reactive; among the alcohols, methanol is the smallest, whereas tert-butanol is so bulky that it adds only with great difficulty. Pairing the least hindered aldehyde with the least hindered alcohol, formaldehyde with methanol gives the cleanest and fastest acetal formation.

JEE Main · 2019 · 12 Jan 2019 · Shift 1 · Single correct option

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