MCQ Detailed View

Grignard reagents (R–MgX) are highly reactive organometallic compounds that react with many electrophiles to form alcohols after hydrolysis. The type of alcohol produced depends on the reactant. When the reactant is formaldehyde or ethylene oxide, the product is a straight-chain alcohol.

1. 
   

   Reaction with Formaldehyde (H–CHO):

   
   
   
   
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     Grignard reagent attacks the carbonyl carbon of formaldehyde.

     
     
   
   
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     After acid hydrolysis, the product is always a primary alcohol of the form R–CH₂OH.

     
     
   
   
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     Since the carbon skeleton of the alkyl group R is directly extended by one carbon atom, the alcohol remains straight-chain.

     
     
   
   
   
   

   Example:
   CH₃–MgBr + H–CHO → CH₃–CH₂–OMgBr → (hydrolysis) → CH₃–CH₂–OH (ethanol)

   
   


2. 
   

   Reaction with Ethylene Oxide (epoxide):

   
   
   
   
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     The carbon atom of the Grignard reagent opens the strained three-membered epoxide ring.

     
     
   
   
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     The ring opening adds a –CH₂–CH₂–OH group to the R group.

     
     
   
   
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     After hydrolysis, this produces a primary alcohol extended by two carbons in a straight chain.

     
     
   
   
   
   

   Example:
   CH₃–MgBr + (CH₂–O–CH₂) → CH₃–CH₂–CH₂–OMgBr → (hydrolysis) → CH₃–CH₂–CH₂–OH (propanol)

   
   


3. 
   

   Reaction with Ketones:

   
   
   
   
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     Gives secondary alcohols, not straight-chain primary alcohols.

     
     
   
   
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     The product depends on the structure of the ketone and the R group of the Grignard reagent.

     
     
   
   
   
   

Thus, only formaldehyde and ethylene oxide give straight-chain primary alcohols upon reaction with a Grignard reagent followed by hydrolysis.

Correct option: Both A & C.