Final answer:
The C=O bond in aldehydes and ketones is typically more readily reduced by catalytic hydrogenation or metallic hydride reagents, turning into alcohols via hydrogen addition or nucleophilic addition of hydride ions.
Step-by-step explanation:
When considering which C bond is more readily reduced by catalytic hydrogenation or metallic hydride reagents, the C=C bond and the C=O bond behave differently. During catalytic hydrogenation, hydrogen gas (H2) is used to reduce both types of bonds in the presence of a metal catalyst, such as nickel (Ni), palladium on carbon (Pd/C), or platinum on carbon (Pt/C). Specifically, the reduction of aldehydes and ketones through catalytic hydrogenation involves the hydrogenation of the C=O bond to form an alcohol.
In the case of reactions with metallic hydride reagents, like sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4), the C=O bond is selectively targeted, leading to the formation of the corresponding alcohol through nucleophilic addition of a hydride ion. Thus, the C=O bond in aldehydes and ketones is typically reduced to a C-OH group by such reagents.