Tetrahydroborate ion is the source of_______________?
Correct answer: D. H-
- A. proton
- B. H+
- C. both A & amp; B
- D. H-
Explanation
The tetrahydroborate ion, BH4-, supplies hydride, H-, which attacks the carbonyl carbon and reduces aldehydes or ketones to alcohols. Students may choose H+ because reduction is often associated with addition of hydrogen, but the hydrogen transferred in this reagent's mechanism is hydride, not a proton.
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About Reactivity of Aldehydes and Ketones
The polar carbonyl group makes aldehydes and ketones undergo nucleophilic addition, reduction and condensation reactions. Aldehydes are generally more reactive and oxidise readily to carboxylic acids, whereas ketones resist mild oxidation; reactions with hydrogen cyanide, sodium bisulfite and 2,4-DNP help identify their behaviour.
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