Question

When a nucleophile encounters a ketone the site of attack is

• A. the carbon atom of the carbonyl
• B. the oxygen atom of the carbonyl
• C. Both the carbon and oxygen atoms with equal probability
• D. no attack occurs - ketones do not react with nucleophiles

Hint:

Nucleophiles attack the electrophilic carbonyl carbon, not the oxygen.

Answer 1

The Correct Option is A

The question given pertains to organic chemistry, specifically to the interaction between nucleophiles and ketones. A ketone is characterized by a carbonyl group (C=O), where the carbon atom is double-bonded to an oxygen atom.

The nature of the carbonyl group is such that the carbon atom carries a partial positive charge due to the electronegativity difference between carbon and oxygen. Oxygen being more electronegative pulls the shared electron density towards itself, resulting in a dipole moment. This makes the carbon atom electrophilic, meaning it is an electron-deficient site and is susceptible to attack by nucleophiles.

Step-by-step Explanation:

1. Identify the Site of Electrophilicity: In the carbonyl group of a ketone, the carbon atom is the electrophilic center due to the polarization of the carbonyl bond. The oxygen atom pulls electron density away from the carbon, making the carbon atom partially positive.
2. Nucleophile's Role: A nucleophile is an electron-rich species that seeks out positive or deficient areas to donate its electrons. Therefore, the partially positive carbon atom in the carbonyl group is its target.
3. Attack Mechanism: The nucleophile approaches and attacks the carbon atom of the carbonyl, forming a new bond between the nucleophile and carbon. The pi-electrons from the C=O bond then shift toward the oxygen atom, temporarily relieving the electrophilicity of the carbon.

Conclusion: The site of nucleophilic attack in a ketone is specifically the carbon atom of the carbonyl group.

Given these explanations, the correct answer is: the carbon atom of the carbonyl.