Organic Chemistry : Using Sodium Borohydride
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Example Questions
Example Question #1 : Organic Reducing Agents
As a reducing agent, 
proton
hydrogen molecule
hydride ion
hydrogen atom
electron
hydride ion
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.
Example Question #1 : Organic Reducing Agents
Which of the following reaction conditions will selectively reduce the ketone in the following compound, retaining the alkene functionality?
Pd, BaSO4, and H2 in hexanes
CeCl3 and NaBH4 in MeOH
LiAlH4 in THF
NaBH4 in MeOH
Pd and H2 in hexanes
CeCl3 and NaBH4 in MeOH
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.
Example Question #2 : Organic Reducing Agents
Which of these can be reduced by sodium borohydride?
Propanoic acid
2-butanol
None of these
3-pentanone
2-butene
3-pentanone
Sodium borohydride is a reducing agent with formula 
Example Question #3 : Organic Reducing Agents
Which of the following statements is false?
None of these
None of these
These are all true uses of 
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