Question

Reaction of butanone with methylmagnesium bromide followed by hydrolysis gives:

• A. 2-methyl-2-butanol
• B. 2-butanol
• C. 3-methyl-2-butanol
• D. 2,2-dimethyl-1-butanol
• E. 2-pentanol

Hint:

To quickly find the product of a Grignard reaction: Formaldehyde gives \(1^\circ\) alcohols, other Aldehydes give \(2^\circ\) alcohols, and Ketones always give \(3^\circ\) alcohols.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
This is a nucleophilic addition reaction of a Grignard reagent (\(\text{R-MgX}\)) to a ketone. Grignard reagents react with ketones to produce tertiary (\(3^\circ\)) alcohols after acidic hydrolysis.

Step 2: Key Formula or Approach
1. \(\text{Ketone} + \text{R'MgBr} \rightarrow \text{Adduct}\)
2. \(\text{Adduct} + \text{H}_2\text{O/H}^+ \rightarrow 3^\circ \text{ alcohol}\)

Step 3: Detailed Explanation
1. Butanone (Ethyl methyl ketone) has the structure: \(\text{CH}_3-\text{CO}-\text{CH}_2-\text{CH}_3\).
2. Methylmagnesium bromide (\(\text{CH}_3\text{MgBr}\)) provides a nucleophilic methyl group (\(\text{CH}_3^-\)).
3. The \(\text{CH}_3^-\) attacks the carbonyl carbon of butanone. The oxygen becomes \(\text{O-MgBr}\).
4. Upon hydrolysis (\(\text{H}_2\text{O}\)), the \(\text{OMgBr}\) group is converted to an \(\text{OH}\) group.
5. The resulting structure is \(\text{CH}_3-\text{C}(\text{OH})(\text{CH}_3)-\text{CH}_2-\text{CH}_3\).
6. Following IUPAC rules, the longest chain has 4 carbons with a methyl and hydroxyl group at the 2nd position: 2-methyl-2-butanol.

Step 4: Final Answer
The product is 2-methyl-2-butanol.