QUESTION 144 (7 marks)
The pathway begins with 2-bromobutane. Under the specified conditions, route II gives but-2-ene as its major alkene product. Compounds X and Y are organic products.
(a) Name X and classify route I. [2 marks]
(b) Write a balanced equation for route II using condensed structural formulas. [2 marks]
(c) Name Y and give suitable reagents and conditions for its formation from X. [2 marks]
(d) Explain why X and Y respond differently to a further treatment with the same ordinary alcohol oxidant. [1 marks]
Practice marking scheme
Answer
X is butan-2-ol; route I is substitution. Route II: . Y is butan-2-one, formed by heated acidified dichromate. X is oxidised; Y is not oxidised under these ordinary conditions.
Working
Aqueous hydroxide replaces Br with OH, giving a secondary alcohol. Heated ethanolic hydroxide removes HBr to give an alkene. Heated acidified potassium dichromate oxidises the secondary alcohol to its ketone. A ketone does not undergo the same ordinary alcohol oxidation; an orange-to-green change is expected when X is oxidised, but not for Y alone under this model.
Marking criteria
- Names X as butan-2-ol. [1 mark]
- Classifies route I as substitution. [1 mark]
- Gives correct reactant and alkene condensed structures for route II. [1 mark]
- Balances NaBr and water in the elimination equation. [1 mark]
- Names Y as butan-2-one. [1 mark]
- Gives acidified dichromate (or manganate(VII)) and heating for oxidation. [1 mark]
- Explains that X is an oxidisable secondary alcohol whereas Y is a ketone. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.