Answer :
The reaction of a Grignard reagent (R-MgBr) with an ester or diethyl carbonate involves nucleophilic addition and substitution,to form a ketone or tertiary alcohol. Magnesium (Mg) reacts with HCl to produce MgCl₂. Option b is correct.
When a Grignard reagent, R-MgBr, reacts with an ester or diethyl carbonate, it follows a nucleophilic addition and substitution mechanism. The nucleophilic carbon of the Grignard reagent attacks the electrophilic carbonyl carbon in the ester or carbonate. This leads to the formation of a tetrahedral intermediate, which upon protonation and elimination of the Mg(OH)Br fragment, results in the formation of a ketone or tertiary alcohol, respectively.
a. Magnesium (Mg) reacts with hydrochloric acid (HCl) to produce magnesium chloride (MgCl₂) and hydrogen gas (H₂).
Mg + 2HCl → MgCl₂ + H₂.
b. Excess Grignard reagent reacting with HCl or water (proton source) can lead to a side reaction where the Grignard reagent is quenched by protonation, preventing its desired reaction with the carbonyl compound.
c. Triarylmethane ions exhibit charge stability through resonance structures. The charge on the ion can be delocalized over the aromatic rings, creating resonance structures where the charge is distributed across different carbon atoms. This delocalization increases the stability of the ion, making it less reactive and more likely to persist in a reaction.
In summary, the reaction of Grignard reagents with esters or carbonates involves nucleophilic addition and substitution, while reactions with Mg, HCl, and excess Grignard reagent with HCl or water have specific outcomes. Resonance structures contribute to the stability of triarylmethane ions by dispersing the charge across aromatic rings.
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