Nucleophilic Addition Reaction:
Aldehyde and ketones are unsaturated compounds hence they show nucleophilic addition reactions.
Mechanism of Nucleophilic Addition Reactions:
The reason for the activity of aldehyde and ketone is due to the presence of polar >C=O bond in them. As oxygen is more electronegative hence it attracts electron density towards it therefore partial negative charge develops on it, on the other hand, partial positive charge develops on a carbon atom.
For initiating the reaction a nucleophile attacks positively charged carbon atom and an intermediate is formed which further convert into the product after the attack of H+. A nucleophile attacks the electrophilic carbon atom of the polar carbonyl group from a direction approximately perpendicular to the plane of sp2 hybridised orbitals of a carbon atom.
The hybridisation of carbon changes from sp2 to sp3 in this process a tetrahedral alkoxide intermediate is formed. This intermediate capture a proton from the reaction medium to give the electrically neutral product. The net result is the addition of Nu– and H+ across the carbon-oxygen double bond. This reaction is named as nucleophilic addition reaction due to an attack of nucleophile in the slow step of the reaction.