Final answer:
In acid-catalyzed hydration of alkenes, water adds across the double bond of an alkene to form an alcohol, often following Markovnikov's rule, resulting in the formation of a chiral center that can be a mix of R and S configurations unless a chiral catalyst is used.
Step-by-step explanation:
The stereochemical outcome of an acid-catalyzed hydration reaction typically involves the addition of water (H2O) across the double bond of an alkene to form an alcohol. During this reaction, one of the hydrogen atoms from the water molecule adds to one of the carbon atoms of the double bond, and the hydroxyl group (OH) adds to the other carbon atom.
The reaction proceeds through the formation of a carbocation intermediate, which is why the more substituted carbon (the carbon with more alkyl groups) is typically where the hydroxyl group attaches, a process known as Markovnikov's rule.
This rule explains that in such addition reactions, the rich get richer—the carbon atom that already has more hydrogens gets bonded to the hydrogen from the water, leaving the other carbon to bond with the hydroxyl group.
In cases where the carbocation can lead to the formation of a chiral center, the reaction will usually be regioselective but not necessarily stereoselective without the presence of a chiral catalyst. That is, the addition can lead to a mix of both R and S configurations of the chiral center in the absence of a stereoselective mechanism.
However, enzyme-catalyzed hydration reactions, like the hydration of fumarate by the enzyme fumarase, demonstrate high stereoselectivity, leading to a single stereoisomer product, such as (S)-malate.