Question

Which of the following compounds on reaction with Grignard reagent followed by hydrolysis forms secondary alcohol?

• A. $\text{CH}_3\text{CHO}$
• B. HCHO
• C. $\text{CH}_3\text{CH}_2\text{COCH}_3$
• D. $\text{CH}_3\text{COCH}_3$

Hint:

Memorize the carbonyl-Grignard map: $\text{Formaldehyde} \rightarrow 1^\circ$ alcohol $\text{Any other Aldehyde} \rightarrow 2^\circ$ alcohol $\text{Ketone} \rightarrow 3^\circ$ alcohol This eliminates wrong choices instantly!

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to identify which carbonyl compound reacts with a Grignard reagent (R-MgX), followed by an acid hydrolysis step, to produce a secondary ($2^\circ$) alcohol.

Step 2: Key Formula or Approach:
Nucleophilic addition of Grignard reagents to carbonyl groups follows a predictable structural pattern:

• $\text{Formaldehyde (HCHO)} + \text{R-MgX} \rightarrow \text{Primary Alcohol } (1^\circ)$

• $\text{Other Aldehydes (R'CHO)} + \text{R-MgX} \rightarrow \text{Secondary Alcohol } (2^\circ)$

• $\text{Ketones (R'COR'')} + \text{R-MgX} \rightarrow \text{Tertiary Alcohol } (3^\circ)$


Step 3: Detailed Explanation:
Let's evaluate the given options based on this general rule:

• Option (A) $\text{CH}_3\text{CHO}$ (Acetaldehyde): This is an aldehyde other than formaldehyde. When attacked by a Grignard reagent ($\text{R}^-$), the nucleophile adds to the carbonyl carbon, producing a secondary alkoxide intermediate. Upon subsequent hydrolysis, it yields a secondary alcohol: $$ \text{CH}_3\text{CHO} + \text{R-MgX} \xrightarrow{\text{hydrolysis}} \text{CH}_3\text{-CH(OH)-R} \quad (\text{Secondary alcohol}) $$

• Option (B) HCHO (Formaldehyde): Yields a primary alcohol because the carbonyl carbon is only bound to hydrogens initially.

• Options (C) and (D) ($\text{CH}_3\text{CH}_2\text{COCH}_3$ and $\text{CH}_3\text{COCH}_3$): These are ketones (Ethyl methyl ketone and acetone). Reaction with Grignard reagents provides tertiary alcohols.


Step 4: Final Answer:
Acetaldehyde ($\text{CH}_3\text{CHO}$) yields a secondary alcohol upon reacting with a Grignard reagent followed by hydrolysis, matching option (A).