2024 H2 Chem P1 Q18 — Introduction to Organic Solution
Question
3-ethylpentan-3-ol is produced when \(C_2H_5MgBr\) is added to pentan-3-one, followed by the addition of aqueous acid.
Which statement about the behaviour of \(C_2H_5^-\) ions in this reaction is correct?
Video Solution
Explanation
The answer is D.
The \(\text{C}_2\text{H}_5^-\) ion uses the lone pair on its carbon to attack the \(\delta+\) carbonyl carbon of pentan-3-one (nucleophilic addition, like the attack of \(\text{CN}^-\) on a carbonyl compound). The alkoxide formed is then protonated by the aqueous acid to give 3-ethylpentan-3-ol. Donating an electron pair makes \(\text{C}_2\text{H}_5^-\) a Lewis base (it acts as a nucleophile).
• A is wrong: an electrophile accepts an electron pair, but \(\text{C}_2\text{H}_5^-\) donates one.
• B is wrong: an Arrhenius base produces \(\text{OH}^-\) ions in water; \(\text{C}_2\text{H}_5^-\) forms no \(\text{OH}^-\) in this reaction.
• C is wrong: a Brønsted-Lowry base accepts \(\text{H}^+\); here \(\text{C}_2\text{H}_5^-\) accepts no proton, it forms a new C-C bond to the carbonyl carbon.
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