Carbonyl groups react via nucleophilic addition, with the mechanism being represented as follows:
The nucleophile attacks the Carbon that is attached to the Oxygen as this will be slightly δ+ due to the difference in electronegativity. This would result in the double bond breaking and the electrons moving towards the Oxygen, creating a negatively charged Oxygen.
This Oxygen can then take a proton (H+) from solution, either from an acid if the solution is acidic or from water if there are no protons available, to produce an alcohol.
Practice Problems – Nucleophilic Addition