In a Grignard reaction, what is the key bond that is formed during the reaction?

• A. A $C–\mathrm{Mg}$ bond
• B. A $C–C$ bond
• C. A $C–H$ bond
• D. A $C–O$ bond

Answer: (B)

Verified step by step guidance

1. Understand that a Grignard reagent is typically an organomagnesium compound with a carbon-magnesium bond, represented as \(\mathrm{C{-}Mg}\).
2. Recognize that the Grignard reagent acts as a nucleophile, where the carbon attached to magnesium carries a partial negative charge and attacks electrophilic centers.
3. In the key step of the Grignard reaction, the nucleophilic carbon attacks a carbonyl carbon (such as in an aldehyde or ketone), leading to the formation of a new carbon-carbon bond.
4. This new \(\mathrm{C{-}C}\) bond formation is crucial because it extends the carbon skeleton, allowing the synthesis of more complex molecules.
5. After the nucleophilic attack and bond formation, protonation (usually by adding water or acid) converts the intermediate into an alcohol, completing the reaction.