Final answer:
The stereochemistry of the product from carbonyl hydride reduction varies depending on the mechanism and can result in the formation of either achiral alcohols, a racemic mixture, or predominantly one enantiomer if chiral catalysts or agents are used.
Step-by-step explanation:
The stereochemistry of a product formed from carbonyl hydride reduction depends on the mechanism of the reaction and the stereochemical outcomes can vary. When aldehydes or ketones are reduced, a hydride ion (H-) adds to the electrophilic carbon of the C=O group, converting it into a hydroxyl group (C-OH).
This process is called nucleophilic addition. For example, reduction of an aldehyde will form a primary alcohol, and reduction of a ketone will form a secondary alcohol.
Regarding the stereochemistry involved, for achiral ketones and aldehydes, the addition of hydride does not create a stereocenter. However, in the reduction of chiral aldehydes or ketones, the reaction is generally not stereoselective unless a chiral reagent or catalyst is used, which could lead to a predominance of one enantiomer over the other.
For instance, the enzyme-catalyzed reactions are stereospecific as the enzyme's active site has a specific 3D shape that favors the formation of one enantiomer. In such biological systems, coenzymes like NAD+ or NADP+ are often involved in the redox reactions instead of a metal catalyst.
In a general chemical synthesis, stereoselectivity can also be achieved using chiral reducing agents or catalysts, allowing for the selective formation of one enantiomer.
As a result, the stereochemistry of the reduction products can vary from non-enantioselective, resulting in a racemic mixture, to highly enantioselective, yielding a single enantiomer predominantly.