Final answer:
Adding a base to a carbonyl reaction increases the rate due to the formation of hydroxide ions from base ionization. These ions act as nucleophiles that can attack the electrophilic carbon, accelerating the nucleophilic addition of water.
Step-by-step explanation:
Adding a base to a reaction involving the addition of water to a carbonyl group increases the rate of the reaction. This is because bases ionize in water, forming hydroxide (OH-) ions. These ions are nucleophilic and can attack the electrophilic carbon of the carbonyl group, thereby facilitating the nucleophilic addition of water. In the carbonyl group, oxygen is more electronegative than carbon, which makes the oxygen slightly negative (nucleophile) and the carbon slightly positive (electrophile). Subsequently, the oxygen's lone pair of electrons contributes to its base character.
Base ionization reaction in water typically involves the transfer of protons from water molecules to base molecules. The presence of hydroxide ions increases the pH of the solution and also provides a conducive environment for the reaction by removing protons from the solution. This is seen in the reaction where B represents the base and BH+ is the conjugate acid; carbonates also follow this trend, acting as moderately strong bases that accept hydrogen ions from water.
The base hence acts as a nucleophile, or oxide donor, in the reaction with the carbonyl group, increasing the likelihood of water addition to the carbonyl group.