Organic Chemistry Questions and Answers – Tautomerism

This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Tautomerism”.

1. How many enolisable hydrogens are there in the following compound?
The enolisable hydrogens in the compound 4
a) 4
b) 5
c) 6
d) 7
View Answer

Answer: a
Explanation: The hydrogen atom present on the carbon which is adjacent to the carbon attached to the functional group, and here it is 4.

2. How many tautomers can you draw for the following ketone?
Find the tautomers for the following ketone
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: b
Explanation: Two isomers can be drawn as shown below:The tautomers for the following ketone is 2

3. How many tautomers can you draw for the following ketone?
Tautomers drawn for the following ketone is 2
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: b
Explanation: Two isomers can be drawn as shown below.
Two isomers can be drawn in given diagram
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4. Which of the following is a tautomer of phenol?
a) The following is a tautomer of phenol - option a
b) The following is a tautomer of phenol - option b
c) The following is a tautomer of phenol - option c
d) The following is a tautomer of phenol - option d
View Answer

Answer: c
Explanation: According to the tautomerism the tautomer of phenol is c.The tautomerism the tautomer of phenol is c

5. Which of the following compound exhibit tautomerism?
Find the following compound exhibit tautomerism
a) I
b) II
c) I and II
d) Neither I nor II
View Answer

Answer: c
Explanation: For Keto-Enol tautomerism, keto form should have α-hydrogen.Keto-Enol tautomerism keto form should have α-hydrogen

6. In keto-enol from presence of which type of hydrogen is must?
a) Alpha
b) Beta
c) Gamma
d) Any position of hydrogen
View Answer

Answer: a
Explanation: For Keto-Enol tautomerism, keto form should have α-hydrogen, as shown in below example.
Alpha type of hydrogen is must in keto-enol in given diagram

7. Which of the following tautomeric form is more stable?

CH3-CH=O   ↔   CH2=C-OH 
      (I)                         (II)
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a) I
b) II
c) Both are equally stable
d) Both are unstable
View Answer

Answer: a
Explanation: The keto–enol tautomerization chemical equilibrium is highly thermodynamically driven, and at room temperature the equilibrium heavily favors the formation of the keto form.

8. What is the stability order for the following compounds?
Find the stability order for the following compounds
a) I > II > III
b) II > I > III
c) III > II > I
d) I > III > II
View Answer

Answer: b
Explanation: The keto–enol tautomerization, less stable enolate ion will be formed faster as it is thermodynamically stable, so III is more stable than I.
II is most sable as it is keto form.
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9. What is the stability order for the following compounds?
Find the stability order for the following compounds
a) I > II > III
b) II > III > I
c) III > II > I
d) I > III > II
View Answer

Answer: b
Explanation: The keto–enol tautomerization, less stable enolate ion will be formed faster as it is thermodynamically stable, so III is more stable than I. II is most stable as it is keto form.

10. Which of the following structure can show tautomerism?
The following structure can show tautomerism is II
a) I
b) II
c) III
d) I and III
View Answer

Answer: b
Explanation: Quinone has an α-hydrogen; however, it is a vinylic hydrogen (hydrogen attached to a carbon atom which is sp2 hybridized), it is very difficult to abstract such a hydrogen, and hence it becomes very less acidic. Therefore, no abstraction of α-hydrogen from it, by a base, hence, it does not show tautomerism, same is for III.

Sanfoundry Global Education & Learning Series – Organic Chemistry.

To practice all areas of Organic Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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