Using Sodium Borohydride

These are all true uses of .

The correct choice, CeCl3 and NaBH4 in MeOH, shows reagents know as "Luche conditions," which are able to modify the reactivity of sodium borohydride to reduce the carbonyl to an alcohol without affecting alkene groups. This occurs as the cerium ion coordinates strongly to the carbonyl oxygen, which subsequently greatly enhances the electrophilicity at the carbonyl carbon. Nucleophilic attack of the hydride readily occurs, simultaneously destroying the electropilicty of the beta carbon of the alkene, such that it will not be reduced by the hydride reagent.

The incorrect answer choices would give various undesired products as detailed below:

NaBH4 in MeOH

Use of unmodified sodium borohydride would result in a 1,4 conjugate addition reaction, saturating the alkene, with a subsequent reduction of the ketone to an alcohol.

LiAlH4 in THF

Use of lithium aluminum hydride would give the same product as use of unmodified sodium borohydride, following the same reduction mechanism.

Pd and H2 in hexanes

This reagent will give reduction of the alkene only.

Pd, BaSO4, and H2 in hexanes

This reagent combination, known as Lindlar's catalyst, will also reduce the alkene only. This reagent is typically used to selectively reduce an alkyne to an alkene.

Sodium borohydride donates a hydride ion to a ketone or aldehyde. In order to form a ketone or aldehyde, a nucleophile must attack the carbonyl group. This is because the ketone or aldehyde has an electrophilic carbon—a nucleophile must attack it in order for any reaction to occur. A hydride ion is the only answer choice that plays the role of a nucleophile.

Sodium borohydride is a reducing agent with formula . It is a reducing agent, but it is not extremely strong. It reduces ketones to alcohols, but it does not affect carboxylic acids. 3-pentanone is the only ketone of the given choices. It would be reduced to 3-pentanol.