MCQ Detailed View

Grignard reagents are versatile organometallic compounds used widely in organic synthesis to form new carbon–carbon bonds. Their general formula is R–MgX, where R is an alkyl or aryl group and X is a halogen. When they react with carbonyl compounds such as aldehydes and ketones, alcohols are produced after hydrolysis.

In this case, the Grignard reagent is ethyl magnesium bromide (C₂H₅MgBr) and the carbonyl compound is acetone (CH₃–CO–CH₃), a ketone. The reaction mechanism proceeds as follows:

1. 
   

   The ethyl group (C₂H₅⁻) in the Grignard reagent behaves as a nucleophile.

   
   


2. 
   

   It attacks the electrophilic carbonyl carbon in acetone, breaking the double bond.

   
   


3. 
   

   This results in the formation of an intermediate alkoxide ion.

   
   


4. 
   

   On hydrolysis with dilute acid, the alkoxide ion is protonated to yield an alcohol.

   
   

Since acetone is a ketone, the nucleophilic addition of the ethyl group produces a carbon atom bonded to three different alkyl groups (two methyl groups from acetone and one ethyl group from the Grignard reagent). This leads to the formation of a tertiary alcohol.

The general rule is:

• 
  

  Formaldehyde + Grignard reagent → Primary alcohol

  
  


• 
  

  Other aldehydes + Grignard reagent → Secondary alcohol

  
  


• 
  

  Ketones + Grignard reagent → Tertiary alcohol

  
  

This is why acetone, being a ketone, always leads to the production of a tertiary alcohol. Such reactions are highly important in laboratory synthesis of complex alcohols and in pharmaceutical chemistry.

Thus, the correct answer is tertiary alcohol.