MCQ Detailed View

Grignard reagents, with the general formula R–MgX (where R is an alkyl or aryl group and X is a halogen), are among the most versatile tools in organic synthesis. Their exceptional reactivity arises mainly from the unique nature of the carbon–magnesium bond.

In the C–Mg bond, magnesium is less electronegative compared to carbon. As a result, the bond is highly polar, with carbon acquiring a partial negative charge (δ–) and magnesium acquiring a partial positive charge (δ+). This polarity makes the carbon atom in Grignard reagents strongly nucleophilic, enabling it to attack electrophilic centers such as the carbonyl carbon in aldehydes, ketones, and esters.

The presence of this carbanion-like character is what makes Grignard reagents highly reactive toward a wide variety of compounds, including water, alcohols, carbon dioxide, and even oxygen from air. For this reason, Grignard reactions must be carried out in strictly anhydrous conditions, typically in dry ether, to prevent premature reaction with moisture.

Looking at the options:

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  The halogen atom (X) plays a stabilizing role but does not directly cause the high reactivity.

  
  


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  The magnesium atom is essential for bond formation, but it is the polarity of the bond rather than its mere presence that drives reactivity.

  
  


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  The correct explanation lies in the C–Mg bond polarity, which imparts the nucleophilic character to carbon.

  
  

Because of this strong nucleophilicity, Grignard reagents are used for forming carbon–carbon bonds, producing alcohols, acids, and other organic products that are key in synthesis.

Thus, the high reactivity of Grignard reagents is best explained by the polarity of the C–Mg bond.