This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses 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
Explanation: 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.
Explanation: 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
Explanation: 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?
b) 2,4- Hexanedione
c) 2, 3-Hexanedione
d) 2, 5-Hexanedione
Explanation: 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.
5. Which of the following will fail to react with potassium dichromate and dilute sulphuric acid?
a) Ethyl alcohol (ethanol)
b) Acetaldehyde (ethanal)
c) Secondary propyl alcohol (2-propanol)
d) Acetone (propanone)
Explanation: Acetone oxidise by K2Cr2O7 & conc. H2SO4 into carboxylic acid. It is not oxidised by dilute H2SO4.
6. Which of the following reactions give benzophenone?
a) 2C6H6 + CCl4 + AlCl3 + H2O→
b) C6H6 + C6H5COCl + AlCl3→
c) o−CH3C6H4COC6H5 + Heat→
d) o−HOOC−C6H4−COC6H5 + Cu260oC→
Explanation: The C6H6 + C6H5COCl + AlCl3→ reaction is a Friedel craft acylation and the mechanism is as follow, which give benzophenone.
7. Which of the following statements regarding chemical properties of acetophenone are wrong?
I. It is reduced to methyl phenyl carbinol by sodium and ethanol
II. It is oxidised to benzoic acid with acidified KMnO4
III. It does not undergo iodoform electrophilic substitution like nitration at meta position
IV. It does not undergo iodoform reaction with iodine and alkali
a) I and II
b) II and IV
c) III and IV
d) I and III
Explanation: It undergoes electrophilic substitution at m-position and also gives iodoform test.
8. The product(s) obtained via oxymercuration (HgSO4+H2SO4) of 1-butyne would be what?
c) CH3CH2CHO + HCHO
d) CH3CH2COOH + HCOOH
Explanation: The product(s) obtained via oxymercuration (HgSO4+H2SO4) of 1-butyne would be what?) of 1-butyne is butan-2-one.
9. Benzophenone does not react with which of the following compound?
Explanation: Except Na2CO3 benzophenone react with rest of options.
10. The conversion of acetophenone to acetanilide is best accomplished by using which reaction?
a) Backmann rearrangement
b) Curtius rearrangement
c) Lossen rearrangement
d) Hofmann rearrangement
Explanation: The conversion of acetophenone to acetanilide is best accomplished by using Backmann rearrangement.
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