"Are
You a Pericyclic Pro? Test Yourself with These MCQs on Pericyclic reactions"
1.
Which
of the following is a pericyclic reaction?
A. Friedel-Crafts alkylation
B. Hofmann degradation
C. Diels-Alder reaction
D. Wittig reaction
Answer: C.
Diels-Alder reaction
2. Which of the following statements
about pericyclic reactions is true?
A. They only involve cyclic transition states.
B. They are always exothermic.
C. They can be either thermally or photochemically induced.
D. They are always concerted reactions.
Answer: C. They
can be either thermally or photochemically induced.
3. Which of the following pericyclic
reactions is an example of an electrocyclic reaction?
A. Diels-Alder reaction
B. Sigmatropic rearrangement
C. Cycloaddition reaction
D.
Cycloreversion reaction
Answer: D.
Cycloreversion reaction
4. Which of the following pericyclic
reactions is an example of a cycloaddition reaction?
A. Sigmatropic rearrangement
B.
Electrocyclic reaction
C. Diels-Alder reaction
D.
Cycloreversion reaction
Answer: C.
Diels-Alder reaction
5. What is the Woodward-Hoffmann rule?
A. It predicts the stereochemistry of
pericyclic reactions.
B. It predicts the regiochemistry of
pericyclic reactions.
C. It relates the symmetry of the
reactants to the symmetry of the transition state.
D. It describes the mechanism of
pericyclic reactions.
Answer: C. It
relates the symmetry of the reactants to the symmetry of the transition state.
6. Which of the following is not a type
of pericyclic reaction?
A. Electrocyclic reaction
B.
Cycloaddition reaction
C. Cycloreversion reaction
D.
Substitution reaction
Answer: D.
Substitution reaction
7. Which of the following is true of the
Diels-Alder reaction?
A. It is a cycloaddition reaction.
B. It
always forms a six-membered ring.
C. It is always an exothermic reaction.
D. It cannot be catalyzed by transition metals.
Answer: A. It is
a cycloaddition reaction.
8. Which of the following is not a
factor that influences the rate of a pericyclic reaction?
A. The reaction temperature
B. The
concentration of the reactants
C. The reaction solvent
D. The molecular
geometry of the reactants
Answer: B. The
concentration of the reactants
9. Which of the following pericyclic
reactions is an example of a sigmatropic rearrangement?
A. Diels-Alder reaction
B. Electrocyclic
reaction
C. Cycloaddition reaction
D. Claisen
rearrangement
Answer: D.
Claisen rearrangement
10. Which of the following pericyclic
reactions is an example of a cycloreversion reaction?
A. Claisen rearrangement
B. Cope
rearrangement
C. Retro-Diels-Alder reaction
D.
Diels-Alder reaction
Answer: C.
Retro-Diels-Alder reaction
11. Which of the following is not a
requirement for a pericyclic reaction to occur?
A. The reaction must be concerted.
B.
The reaction must have a cyclic transition state.
C. The reaction must be exothermic.
D.
The reaction must obey the Woodward-Hoffmann rules.
Answer: C. The
reaction must be exothermic.
12. Which of the following pericyclic
reactions is an example of a [1,5] sigmatropic rearrangement?
A. Cope rearrangement
B. Claisen
rearrangement
C. Carroll rearrangement
D. Brook
rearrangement
Answer: A. Cope
rearrangement
13. Which of the following pericyclic
reactions is an example of a [3,3] sigmatropic rearrangement?
A. Claisen rearrangement
B. Brook
rearrangement
C. Enone-ene reaction
D. Ireland-Claisen
rearrangement
Answer: A.
Claisen rearrangement
14. Which of the following is not a type
of pericyclic reaction?
A. Rearrangement reaction
B. Cycloaddition
reaction
C. Cycloreversion reaction
D.
Electrocyclic reaction
Answer: A.
Rearrangement reaction
15. Which of the following is not a
requirement for a pericyclic reaction to be thermally allowed?
A. The reaction must obey the
Woodward-Hoffmann rules.
B. The reaction must have a cyclic
transition state.
C. The reactants must have the correct
symmetry.
D. The reaction must have a large
negative entropy of activation.
Answer: D. The
reaction must have a large negative entropy of activation.
16. Which of the following pericyclic reactions is an example of an electrocyclic reaction?
A. Diels-Alder reaction
B. Cope rearrangement
C. Retro-ene reaction
D. Ireland-Claisen rearrangement
Answer: B. Cope
rearrangement
17. Which of the following pericyclic
reactions is an example of a photochemical reaction?
A. Cope rearrangement
B. Claisen
rearrangement
C. Diels-Alder reaction
D. Sigmatropic
rearrangement
Answer: C.
Diels-Alder reaction
18. Which of the following pericyclic
reactions is an example of a [3,2] sigmatropic rearrangement?
A. Claisen rearrangement
B. Enone-ene
reaction
C. Ireland-Claisen rearrangement
D.
Brook rearrangement
Answer: C.
Ireland-Claisen rearrangement
19. Which of the following statements
about sigmatropic rearrangements is true?
A. They always involve the migration of
a carbocation.
B. They can only occur through the
formation of a cyclic transition state.
C. They can occur with either retention
or inversion of configuration.
D. They always occur with a change in the
number of pi electrons.
Answer: C. They
can occur with either retention or inversion of configuration.
20. Which of the following pericyclic
reactions is an example of a [1,3] sigmatropic rearrangement?
A. Cope rearrangement
B. Claisen
rearrangement
C. Carroll rearrangement
D. Brook
rearrangement
Answer: C.
Carroll rearrangement
21. Which of the following is not a
factor that can affect the selectivity of a pericyclic reaction?
A. The reaction temperature
B. The
reaction solvent
C. The identity of the catalyst
D. The
geometry of the reactants
Answer: C. The
identity of the catalyst
22. Which of the following pericyclic
reactions is an example of a cycloreversion reaction?
A. Claisen rearrangement
B. Cope
rearrangement
C. Retro-Diels-Alder reaction
D.
Electrocyclic reaction
Answer: C.
Retro-Diels-Alder reaction
23. Which of the following pericyclic
reactions is an example of a [2+2] cycloaddition reaction?
A. Diels-Alder reaction
B. 1,3-dipolar
cycloaddition reaction
C. [2+2] photocycloaddition reaction
D.
[2+2] thermal cycloaddition reaction
Answer: D. [2+2]
thermal cycloaddition reaction
24. Which of the following pericyclic
reactions is an example of a [4+2] cycloaddition reaction?
A. Diels-Alder reaction
B. 1,3-dipolar
cycloaddition reaction
C. [2+2] photocycloaddition reaction
D.
[2+2] thermal cycloaddition reaction
Answer: A.
Diels-Alder reaction
25. Which of the following statements
about electrocyclic reactions is true?
A. They always involve the formation of
a cyclic transition state.
B. They can only occur with fully
conjugated systems.
C. They can occur with either a thermal
or photochemical initiation.
D. They always result in the breaking of
a sigma bond.
Answer: C. They
can occur with either a thermal or photochemical initiation.
26. Which of the following pericyclic reactions is an example of a [1,2] sigmatropic rearrangement?
A. Cope rearrangement
B. Claisen rearrangement
C. Carroll rearrangement
D. Brook rearrangement
Answer: B.
Claisen rearrangement
27. Which of the following statements
about Woodward-Hoffmann rules is true?
A. They are a set of empirical rules
that predict the outcome of pericyclic reactions.
B. They are based on the analysis of
quantum mechanical calculations of pericyclic reactions.
C. They apply only to thermally allowed
pericyclic reactions.
D. They have no practical applications
in organic chemistry.
Answer: A. They
are a set of empirical rules that predict the outcome of pericyclic reactions.
28. Which of the following pericyclic
reactions is an example of a [1,6] sigmatropic rearrangement?
A. Cope rearrangement
B. Claisen rearrangement
C. Carroll rearrangement
D. Brook rearrangement
Answer: D. Brook
rearrangement
29. Which of the following pericyclic
reactions is an example of a [2+2] photocycloaddition reaction?
A. Diels-Alder reaction
B. 1,3-dipolar
cycloaddition reaction
C. [2+2] thermal cycloaddition reaction
D. [4+4] photocycloaddition reaction
Answer: C. [2+2]
thermal cycloaddition reaction
30. Which of the following pericyclic reactions is an example of a thermal [1,5] sigmatropic rearrangement?
A. Cope rearrangement
B. Claisen rearrangement
C. Carroll rearrangement
D. Brook
rearrangement
Answer: C.
Carroll rearrangement
31. Which of the following approaches is
used to predict the outcome of pericyclic reactions?
A. PMO
B. FMO
C. Both A and B
D. None of
the above
Answer: C. Both
A and B
32. In the PMO approach, what do the
coefficients of the molecular orbitals represent?
A. The energy of the orbitals
B. The
electron density of the orbitals
C. The symmetry of the orbitals
D. The
nodal planes of the orbitals
Answer: B. The
electron density of the orbitals
33. Which of the following pericyclic
reactions is symmetry allowed?
A. Electrocyclic ring opening
B. Cope
rearrangement
C. [2+2] cycloaddition
D. [3,3]
sigmatropic rearrangement
Answer: D. [3,3]
sigmatropic rearrangement
34. In the FMO approach, what do the
energies of the molecular orbitals determine?
A. The electron density of the orbitals
B. The stability of the molecule
C. The symmetry of the orbitals
D. The
nodal planes of the orbitals
Answer: B. The
stability of the molecule
35. Which of the following pericyclic
reactions is symmetry forbidden?
A. Electrocyclic ring closure
B. Cope
rearrangement
C. [2+2] cycloaddition
D. [3,3]
sigmatropic rearrangement
Answer: C. [2+2]
cycloaddition
36. Which of the following is not one of
the Woodward-Hoffmann rules?
A. Conservation of orbital symmetry
B. The frontier orbitals of the
reactants control the outcome of the reaction
C. The transition state should be as low
in energy as possible
D. The reaction should be allowed by the
conservation of angular momentum
Answer: C. The
transition state should be as low in energy as possible
37. In a suprafacial reaction, what happens
to the two groups involved in the reaction?
A. They remain on the same side of the molecule
B. They switch sides of the molecule
C. One group moves to the opposite side of the molecule
D. Both groups are removed from the molecule
Answer: A. They
remain on the same side of the molecule
38. Which of the following pericyclic
reactions is an example of an antarafacial process?
A. [1,5] sigmatropic rearrangement
B.
[3,3] sigmatropic rearrangement
C. Electrocyclic ring opening
D. Cope
rearrangement
Answer: B. [3,3]
sigmatropic rearrangement
39. Which of the following pericyclic
reactions is an example of a suprafacial process?
A. [1,5] sigmatropic rearrangement
B.
[3,3] sigmatropic rearrangement
C. Electrocyclic ring closure
D. Cope
rearrangement
Answer: D. Cope
rearrangement
40. In a symmetry allowed pericyclic
reaction, what is conserved?
A. Angular momentum
B. Spin
C. Orbital symmetry
D. Molecular weight
Answer: C.
Orbital symmetry
41. In which type of pericyclic reaction
does the reaction proceed through a cyclic transition state?
A. Electrocyclic reaction
B. Cycloaddition reaction
C. Sigmatropic rearrangement
D. All of the above
Answer: D. All
of the above
42. Which of the following pericyclic
reactions is an example of a thermal reaction?
A. Diels-Alder reaction
B. Photochemical
cycloaddition
C. [1,5] sigmatropic rearrangement
D.
Electrocyclic ring closure
Answer: A.
Diels-Alder reaction
43. Which of the following pericyclic
reactions involves a concerted reaction pathway?
A. Electrocyclic ring opening
B. Diels-Alder reaction
C. Cope rearrangement
D. All of the above
Answer: D. All
of the above
44. In a Diels-Alder reaction, which of
the following orbitals must be in phase?
A. HOMO of diene and LUMO of dienophile
B. LUMO of diene and HOMO of dienophile
C. HOMO of diene and HOMO of dienophile
D. LUMO of diene and LUMO of dienophile
Answer: A. HOMO
of diene and LUMO of dienophile
45. Which of the following is a
characteristic of a concerted pericyclic reaction?
A. The reaction occurs in multiple steps
B. The reaction mechanism involves the
formation of a carbocation intermediate
C. The reaction is not stereospecific
D. The reaction is exothermic
Answer: D. The
reaction is exothermic
46. Which of the following is an example
of a [4+2] cycloaddition reaction?
A. Diels-Alder reaction
B. [1,3] dipolar
cycloaddition
C. [3,2] sigmatropic rearrangement
D.
Cope rearrangement
Answer: A.
Diels-Alder reaction
47. In a sigmatropic rearrangement,
which of the following groups is conserved?
A. The size of the molecule
B. The
stereochemistry of the molecule
C. The electronic configuration of the molecule
D. The functional group of the molecule
Answer: A. The
size of the molecule
48. Which of the following is an example
of an electrocyclic reaction?
A. Cope rearrangement
B. [3,3]
sigmatropic rearrangement
C. Electrocyclic ring opening
D. [1,5]
sigmatropic rearrangement
Answer: C.
Electrocyclic ring opening
49. Which of the following is an example
of a photochemical reaction?
A. Diels-Alder reaction
B. [1,3] dipolar
cycloaddition
C. [3,2] sigmatropic rearrangement
D.
None of the above
Answer: B. [1,3]
dipolar cycloaddition
50. Which of the following is a
characteristic of a symmetry-forbidden pericyclic reaction?
A. The reaction occurs via a cyclic
transition state
B. The reaction is stereospecific
C. The reaction does not follow the
Woodward-Hoffmann rules
D. The reaction involves the
conservation of angular momentum
Answer: C. The
reaction does not follow the Woodward-Hoffmann rules
51. Which of the following is true
regarding nodes in pericyclic reactions?
A. Nodes are regions of high electron
density in the reaction center
B. Nodes are regions of low electron
density in the reaction center
C. Nodes are regions of maximum overlap
between orbitals
D. Nodes are regions of destructive
interference between orbitals
Answer: D. Nodes
are regions of destructive interference between orbitals.
52. Which of the following statements is
true regarding aromatic and antiaromatic molecules in pericyclic reactions?
A. Aromatic molecules always undergo
pericyclic reactions with low activation energy
B. Anti-aromatic molecules always
undergo pericyclic reactions with low activation energy
C. Aromatic molecules follow the
Woodward-Hoffmann rules, while antiaromatic molecules do not
D. Anti-aromatic molecules follow the
Woodward-Hoffmann rules, while aromatic molecules do not
Answer: C.
Aromatic molecules follow the Woodward-Hoffmann rules, while antiaromatic
molecules do not.
53. Which of the following is an example
of a thermal pericyclic reaction?
A. Diels-Alder reaction
B. [1,5]
sigmatropic rearrangement
C. Photochemical [2+2] cycloaddition
D.
[1,3] dipolar cycloaddition
Answer: B. [1,5]
sigmatropic rearrangement.
54. Which of the following is true
regarding photochemical pericyclic reactions?
A. Photochemical reactions always occur
with high stereoselectivity
B. Photochemical reactions always have
high activation energy barriers
C. Photochemical reactions always involve
the breaking of a bond
D. Photochemical reactions can be used
for the synthesis of complex molecules with high efficiency
Answer: D.
Photochemical reactions can be used for the synthesis of complex molecules with
high efficiency.
55. Which of the following statements is
true regarding photochemical pericyclic reactions?
A. Photochemical reactions always
require light of a specific wavelength to occur
B. Photochemical reactions always
involve the formation of a cyclic transition state
C. Photochemical reactions are always
exothermic
D. Photochemical reactions can only
occur in the gas phase
Answer: A.
Photochemical reactions always require light of a specific wavelength to occur.
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