20 challenging multiple-choice questions in organic chemistry focused on isomerism, along with detailed solutions
**Question 1: Isomerism**
How many stereoisomers are possible for 1,2-dichloroethene (C₂H₂Cl₂)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
b) 2
**Question 2: Isomerism**
Which of the following is an example of geometric (cis-trans) isomerism?
a) Ethanol and methanol
b) Butane and isobutane
c) 1,2-dichloroethene and 1,1-dichloroethene
d) Ethene and propene
**Solution:**
c) 1,2-dichloroethene and 1,1-dichloroethene
**Question 3: Isomerism**
How many constitutional isomers are possible for C₅H₁₂ (pentane)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
d) 4
**Question 4: Isomerism**
Which of the following compounds is an example of a structural isomer of butene (C₄H₈)?
a) Isobutene (i-C₄H₈)
b) Butane (C₄H₁₀)
c) Butyne (C₄H₆)
d) Butanal (C₄H₈O)
**Solution:**
d) Butanal (C₄H₈O)
**Question 5: Isomerism**
How many stereoisomers are possible for 2,3-dichlorobutane (C₄H₈Cl₂)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
b) 2
**Question 6: Isomerism**
Which of the following compounds is an example of a structural isomer of 2-methylpropane (C₄H₁₀)?
a) Isobutane (i-C₄H₁₀)
b) Ethane (C₂H₆)
c) Propane (C₃H₈)
d) Butane (C₄H₁₀)
**Solution:**
b) Ethane (C₂H₆)
**Question 7: Isomerism**
How many constitutional isomers are possible for C₆H₁₂O (hexanol)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
c) 3
**Question 8: Isomerism**
Which of the following compounds is an example of a structural isomer of 1,2-dichloroethane (C₂H₄Cl₂)?
a) 1,1-dichloroethane (C₂H₄Cl₂)
b) Ethene (C₂H₄)
c) Ethane (C₂H₆)
d) Chloroethyne (C₂HCl)
**Solution:**
d) Chloroethyne (C₂HCl)
**Question 9: Isomerism**
How many stereoisomers are possible for 3,4-dichloropentane (C₅H₁₀Cl₂)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
c) 3
**Question 10: Isomerism**
Which of the following is an example of tautomeric isomerism?
a) Ethene and propene
b) 1-butanol and 2-butanol
c) Acetaldehyde and acetone
d) Keto form and enol form of a compound
**Solution:**
d) Keto form and enol form of a compound
**Question 11: Isomerism**
How many constitutional isomers are possible for C₅H₁₀O (pentanal)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
c) 3
**Question 12: Isomerism**
Which of the following compounds is an example of a geometric (cis-trans) isomer?
a) Methane (CH₄) and ethane (C₂H₆)
b) Ethanol (C₂H₅OH) and methanol (CH₃OH)
c) Butane (C₄H₁₀) and isobutane (i-C₄H₁₀)
d) 1,2-dichloroethene and 1,1-dichloroethene
**Solution:**
d) 1,2-dichloroethene and 1,1-dichloroethene
**Question 13: Isomerism**
How many stereoisomers are possible for 2,3-dimethylpentane (C₆H₁₄)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
d) 4
**Question 14: Isomerism**
Which of the following compounds is an example of a structural isomer of pentanal (C₅H₁₀O)?
a) Pentanone (C₅H₁₀O)
b) 2-methylbutanal (C₅H₁₀O)
c) Butanal (C₄H₈O)
d) 2,2-dimethylpropanal (C₆H₁₂O)
**Solution:**
c) Butanal (C₄H₈O)
**Question 15: Isomerism**
How many constitutional isomers are possible for C₆H₁₂ (hexane)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
d) 4
**Question 16: Isomerism**
Which of the following compounds is an example of a structural isomer of 1-butene (C₄H₈)?
a) 2-butene (C₄H₈)
b) Butane (C₄H₁₀)
c) Ethene (C₂H₄)
d) Butanal (C₄H₈O)
**Solution:**
d) Butanal (C₄H₈O)
**Question 17: Isomerism**
How many stereoisomers are possible for 2,3-dibromobutane (C₄H₈Br₂)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
b) 2
**Question 18: Isomerism**
Which of the following compounds is an example of a geometric (cis-trans) isomer?
a) Ethanol (C₂H₅OH) and methanol (CH₃OH)
b) Ethane (C₂H₆) and ethene (C₂H₄)
c) Butane (C₄H₁₀) and isobutane (i-C₄H₁₀)
d) 1,2-dichloroethene and 1,1-dichloroethene
**Solution:**
d) 1,2-dichloroethene and 1,1-dichloroethene
**Question 19: Isomerism**
How many constitutional isomers are possible for C₅H₁₀O (pentanol)?
a) 1
b) 2
c) 3
d) 4
**Solution:**
c) 3
**Question 20: Isomerism**
Which of the following compounds is an example of a structural isomer of 2,3-dimethylbutane (C₆H₁₄)?
a) 2,3-dimethylpentane (C₆H₁₄)
b) 3,3-dimethylpentane (C₆H₁₄)
c) 2,2,3-trimethylbutane (C₆H₁₄)
d) 2,3-dimethylhexane (C₆H₁₄)
**Solution:**
c) 2,2,3-trimethylbutane (C₆H₁₄)
These challenging multiple-choice questions focus on isomerism in organic chemistry, and the detailed solutions provide explanations to help you understand the correct answers.
