Organic Chemistry Multiple Choice Questions on “Chemical Properties of Ketones”.
1. Which of the following reaction is not shown by ketones?
a) reaction with HCN
b) reaction with NaHSO3
c) reaction with 2,4-Dinitrophenyl hydrazine
d) reaction with Fehling solution
Answer: d
Clarification: Fehling’s can be used to distinguish aldehyde vs ketone functional groups. The compound to be tested is added to the Fehling’s solution and the mixture is heated. Aldehydes are oxidized, giving a positive result, but ketones do not react, unless they are alpha-hydroxy-ketones.
2. The enol form of acetone, after treatment with D2O, gives which of the following product?
a)
b)
c)
d) 
Answer: b
Clarification: The enol form of acetone on treatment with D2O undergoes enolisation, deutration (addition of D2O) and dehydration (removal of H2O). The repeated enolisation, deutration and dehydration ultimately gives CD3.COCD3.
3. Acetone reacts with HCN to form a cyanohydrin. It is an example of which type of reaction?
a) electrophilic addition
b) electrophilic substitution
c) nucleophilic addition
d) nucleophilic substitution
Answer: c
Clarification: In the reaction, Acetone reacts with HCN to form a cyanohydrin, dissociated proton from HCN activates the carbonyl, which facilitates the nucleophilic attack of CN.
4. Which of the following has most acidic hydrogen?
a) 3-Hexaone
b) 2,4- Hexanedione
c) 2, 3-Hexanedione
d) 2, 5-Hexanedione
Answer: b
Clarification: 2, 4-hexanedione (a 1, 3-diketone) has the most acidic hydrogen. This is because the carbanion left after the removal of H+ is resonance stabilised in this case.
