Nucleophilic Addition to Carbonyl Compounds

• Nucleophilic addition is a fundamental reaction mechanism in organic chemistry, particularly for the reactivity of carbonyl compounds like aldehydes and ketones.
• This process involves a nucleophile attacking an electrophilic center to form a new chemical bond.
• For carbonyl compounds, the electrophilic center is the carbon atom of the carbonyl group (C=O).

Mechanism of Nucleophilic Addition to Carbonyl Compounds

1. Nucleophilic Attack:

   • The nucleophile, with a lone pair of electrons, attacks the electrophilic carbonyl carbon.
   • The carbon is electrophilic due to the polarization of the C=O bond, where the oxygen atom pulls electron density away, making the carbon partially positive (δ+).
   • Equation: Nu⁻ + R-CHO → Nu-R-CHO⁻

2. Formation of a Tetrahedral Intermediate:

   • The attack breaks the π bond of the C=O group, pushing electrons onto the oxygen atom.
   • This forms a tetrahedral intermediate with a negatively charged oxygen (O⁻).
   • Intermediate Formation: Nu-R-CHO⁻

3. Proton Transfer:

   • The negatively charged oxygen in the intermediate abstracts a proton (H⁺) from a proton source (solvent, acid, or conjugate acid of the nucleophile).
   • This step neutralizes the charge on the oxygen, resulting in the formation of an alcohol.
   • Protonation: Nu-R-CHO⁻ + H⁺ → Nu-R-CH(OH)

Example Reaction

• For a generic aldehyde (R−CHO):
  1. Step 1: The nucleophile (Nu⁻) attacks the carbonyl carbon, forming a tetrahedral intermediate.
  2. Step 2: The intermediate captures a proton (H⁺), yielding an alcohol (Nu−R−CH(OH)).

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