What is the product of this reaction? (Note: NaBD4 is the same as NaBH4 where the hydrogens have been replaced by deuterium) NaBD4 H2O CH3OH OH CDCH3 OD CHCH3 OD CDCH3 CH2CO2CH3 A B CH3
The Correct Answer and Explanation is:
Correct Answer: B. CDCH3
Explanation:
The reagent NaBD₄ (sodium borodeuteride) is a deuterated version of NaBH₄ (sodium borohydride), commonly used to reduce carbonyl compounds such as aldehydes and ketones. In NaBD₄, the hydride (H⁻) ions are replaced with deuteride (D⁻) ions. This means during reduction, the D⁻ from NaBD₄ is delivered to the carbonyl carbon instead of H⁻, leading to a product with deuterium.
Let’s break down the reaction step by step:
- Starting Material: CH₃COCH₃ (acetone) is the likely substrate given the context of the product choices. Acetone is a ketone with the structure:
- CH₃—CO—CH₃
- Reagent: NaBD₄ in a protic solvent (e.g. H₂O and CH₃OH). NaBD₄ donates a deuteride ion (D⁻), which attacks the electrophilic carbonyl carbon of acetone.
- Mechanism:
- The deuteride (D⁻) adds to the carbon of the C=O bond.
- The pi electrons from the C=O double bond move to the oxygen, forming an alkoxide intermediate.
- Protonation of the alkoxide occurs from the solvent (H₂O or CH₃OH), delivering an H⁺ (proton) to the oxygen.
- Product: The carbonyl is reduced to a secondary alcohol, and one of the methyl groups is now bonded to a carbon bearing a D (from NaBD₄) and an OH (from solvent protonation). This gives:
- CDCH₃OH or more specifically (CH₃)₂C(OH)D
- Among the answer choices, the only one representing the correct product is B. CDCH₃, since it reflects that one of the methyl groups has been reduced with the incorporation of a deuterium at the central carbon.
Summary:
NaBD₄ reduces carbonyl groups just like NaBH₄, but replaces a hydrogen atom with deuterium. In the case of acetone, this leads to the formation of isopropanol with one D atom, represented by CDCH₃. Hence, the correct answer is B.
