Organic Chemistry MCAT Practice Exam

Which reducing agents are commonly used to reduce carbonyl compounds to alcohols?

1. NaBH4 or LiAlH4

2. H2O or NH3

3. K2Cr2O7 or KMnO4

4. Boranes or alkyl lithium reagents

The correct answer is: NaBH4 or LiAlH4

The choice of reducing agents for converting carbonyl compounds to alcohols hinges on the agents' ability to donate hydride ions. Sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4) are both effective hydride donors that facilitate this reduction reaction. Sodium borohydride is milder and typically used for the reduction of aldehydes and ketones, converting them into their corresponding alcohols without affecting other functional groups. It works under relatively mild conditions, making it ideal for sensitive substrates. Lithium aluminum hydride, on the other hand, is a much stronger reducing agent and can reduce a broader range of carbonyl compounds, including esters and carboxylic acids, to alcohols. Due to its reactivity, it often requires careful handling and an anhydrous environment, as it reacts violently with water. In contrast, the other choices provided consist of reagents that do not serve the same reducing function. Water and ammonia are not reducing agents in this context; instead, they are solvents or reactants that may not facilitate reduction of carbonyls. The compounds potassium dichromate (K2Cr2O7) and potassium permanganate (KMnO4) are