Question 24.6: The electrophilic addition of water to a molecule containing...

The electrophilic addition of water to a molecule containing a double bond, known as hydration, is a reaction that is important biologically. One example is the enzyme-catalyzed hydration of fumarate to form malate, one of the steps in the citric acid cycle (also known as the Krebs cycle).

Using curved arrows to indicate the movement of electrons, draw the mechanism for the electrophilic addition of water to fumarate to yield malate.

Strategy For electrophilic addition, draw Lewis structures with the electrophile close to the region of electron density where attack will occur.

Setup The electrophile is one of the \text{H} atoms in \text{H}_2\text{O}. The site of attack is the pi bond between the \text{C} atoms in fumarate: