The addition of hydrogen cyanide to ethanal gives
Correct answer: B. 2-hydroxypropanenitrile
- A. ethanoic acid
- B. 2-hydroxypropanenitrile
- C. ethanol
- D. propanone
Explanation
The cyanide ion attacks the carbonyl carbon and the resulting alkoxide picks up a proton, giving a hydroxynitrile with one more carbon than the starting aldehyde. The reaction is catalysed by a trace of base, which generates the cyanide nucleophile. The product can be hydrolysed to a hydroxy acid, making this a useful chain lengthening step.
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About Nucleophilic Addition Reactions
Nucleophilic addition occurs at the polar carbonyl group of aldehydes and ketones, where a nucleophile attacks the electron-deficient carbon atom. Reactions with hydrogen cyanide, sodium bisulfite, alcohols and Grignard reagents are explained through tetrahedral intermediates, acid or base catalysis, and the different reactivity of aldehydes and ketones.
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