Question 1

Which of the following statements about a p* antibonding molecular orbital is true?

Accepted Answer

A)  A p* antibonding molecular orbital is formed when two p orbitals of similar phase overlap.
B)  A p* antibonding molecular orbital is formed when two p orbitals of opposite phase overlap.
C)  A p* antibonding molecular orbital is a higher-energy molecular orbital than a p bonding molecular orbital.
D)  Both the statements a p* antibonding molecular orbital is formed when two p orbitals of opposite phase overlap and a p* antibonding molecular orbital is a higher-energy molecular orbital than a p bonding molecular orbital are true.E) A) and D)
F) B) and C)

Question 2

What is the major organic product of the following Claisen rearrangement?

Accepted Answer

A)  I
B)  II
C)  III
D)  IVE) C) and D)
F) B) and C)

Question 3

What is the correct classification of the following reaction?

Accepted Answer

A)  Cycloaddition reaction
B)  Electrophilic reaction
C)  Electrocyclic reaction
D)  Sigmatropic reactionE) A) and B)
F) A) and C)

Question 4

Which of the following statements about orbital symmetry and cycloaddition reactions is true?

Accepted Answer

A)  Thermal cycloadditions involving an even number of p bonds proceed by a suprafacial pathway.
B)  Thermal cycloadditions involving an odd number of p bonds proceed by a suprafacial pathway.
C)  Photochemical cycloadditions involving an odd number of p bonds proceed by a suprafacial pathway.
D)  Photochemical sycloadditions involving an even number of p bonds proceed by an antarafacial pathway.E) All of the above
F) A) and B)

Question 5

Which of the following statements about cycloaddition reactions is true?

Accepted Answer

A)  Cycloaddition reactions can be initiated by heat only.
B)  Cycloaddition reactions can be initiated by light only.
C)  Cycloaddition reactions can be initiated by heat or light.
D)  Cycloaddition reactions are identified by the number of p electrons in the two products.E) A) and D)
F) B) and D) C

Question 6

Which of the following statements about cycloaddition reactions is not true?

Accepted Answer

A)  Cycloaddition reactions form a cyclic product with two new s bonds.
B)  The course of the reaction is determined by the symmetry of the molecular orbitals of the products.
C)  Cycloaddition reactions are concerted.
D)  Cycloaddition reactions are stereospecific.E) B) and C)
F) A) and C)

Question 7

Which of the following statements about thermal electrocyclic reactions is not true?

Accepted Answer

A)  The number of s bonds in the conjugated polyene determines whether rotation is conrotatory or disrotatory.
B)  Thermal electrocyclic reactions occur in a disrotatory fashion for a conjugated polyene with an odd number of p bonds.
C)  Thermal electrocyclic reactions occur in a conrotatory fashion for a conjugated polyene with an even number of p bonds.
D)  In thermal reactions,we consider the orbitals of the HOMO of the ground state electronic configuration to determine the course of the reaction.E) All of the above
F) C) and D)

Question 8

Predict the major organic product(s) of the following electrocyclic reaction.

Accepted Answer

A)  Only I
B)  Only II
C)  Only III
D)  Only I and IIE) A) and B)
F) B) and C)

Question 9

Which of the following statements about photochemical electrocyclic reactions is not true?

Accepted Answer

A)  In photochemical reactions,we consider the orbitals of the HOMO of the excited state to determine the course of the reaction.
B)  Photochemical electrocyclic reactions occur in a conrotatory fashion for a conjugated polyene with an odd number of p bonds.
C)  Photochemical electrocyclic reactions occur in a disrotatory fashion for a conjugated polyene with an even number of p bonds.
D)  In photochemical reactions,we consider the orbitals of the LUMO of the excited state to determine the course of the reaction.E) All of the above
F) A) and B)

Question 10

What is the correct classification of the following reaction?

Accepted Answer

A)  Cycloaddition reaction
B)  Electrophilic reaction
C)  Electrocyclic reaction
D)  Sigmatropic reactionE) A) and B)
F) None of the above

Question 11

Consider the following reaction sequence.What is the correct classification of the first reaction in the sequence?

Accepted Answer

A)  [1,3] Sigmatropic rearrangement
B)  [1,5] Sigmatropic rearrangement
C)  [3,3] Sigmatropic rearrangement
D)  [5,5] Sigmatropic rearrangementE) A) and B)
F) A) and C)

Question 12

Which of the following statements about an electrocyclic ring-opening reaction is not true?

Accepted Answer

A)  An electrocyclic ring-opening reaction is an intramolecular reaction.
B)  An electrocyclic ring-opening reaction requires a source of energy (heat or light) .
C)  The product of an electrocyclic ring-opening reaction contains one fewer p bond than the reactant.
D)  The product of an electrocyclic ring-opening reaction contains one more p bond than the reactant.E) A) and B)
F) All of the above

Question 13

Which of the following statements about pericyclic reactions is not true?

Accepted Answer

A)  Pericyclic reactions are concerted reactions.
B)  Pericyclic reactions proceed through a cyclic transition state.
C)  Pericyclic reactions are not stereospecific.
D)  Pericyclic reactions require light or heat.E) A) and B)
F) A) and C)

Question 14

Which of the following statements about a p-bonding molecular orbital is true?

Accepted Answer

A)  A p-bonding molecular orbital is formed when two p orbitals of similar phase overlap.
B)  A p-bonding molecular orbital is lower in energy than a s-bonding molecular orbital.
C)  A p-bonding molecular orbital is formed when two p orbitals of opposite phase overlap.
D)  Both the statements a p-bonding molecular orbital is formed when two p orbitals of similar phase overlap and a p-bonding molecular orbital is lower in energy than a s-bonding molecular orbital are true.E) All of the above
F) A) and D)

Question 15

Predict the major organic product(s) of the following electrocyclic reaction.

Accepted Answer

A)  Only I
B)  Only II
C)  Only III
D)  Only I and IIE) B) and C)
F) A) and B)

Question 16

What are the two modes of bond formation in cycloaddition reactions?

Accepted Answer

A)  Suprafacial and antarafacial bond formations
B)  Superfacial and antifacial bond formations
C)  Suprafacial and synfacial bond formations
D)  Synfacial and antifacial bond formationsE) A) and D)
F) A) and C) A

Question 17

Which of the following statements about sigmatropic reactions is not true?

Accepted Answer

A)  A sigmatropic reaction is an intramolecular pericyclic reaction.
B)  In a sigmatropic reaction,s bond is broken in one of the reactants.
C)  The p bonds rearrange in a sigmatropic reaction.
D)  The number of p bonds in the reactants and product differs in a sigmatropic reaction.E) A) and D)
F) B) and C)

Question 18

Predict the major organic product(s) of the following electrocyclic reaction.

Accepted Answer

A)  Only I
B)  Only II
C)  Only III
D)  Only I and IIE) A) and B)
F) A) and C)

Question 19

Consider the following reaction sequence.What is the correct classification of the second reaction in the sequence?

Accepted Answer

A)  [2 + 2] Cycloaddition
B)  [6 + 4] Cycloaddition
C)  [4 + 4] Cycloaddition
D)  [4 + 2] CycloadditionE) None of the above
F) B) and C) D

Question 20

What type of sigmatropic rearrangement is illustrated below?

Accepted Answer

A)  [1,3]
B)  [1,4]
C)  [3,3]
D)  [1,5]E) C) and D)
F) None of the above

Exam 25: Pericyclic Reactions

Which of the following statements about a p* antibonding molecular orbital is true?

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What is the major organic product of the following Claisen rearrangement?

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What is the correct classification of the following reaction?

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Which of the following statements about orbital symmetry and cycloaddition reactions is true?

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Which of the following statements about cycloaddition reactions is true?

Correct AnswerverifiedC

Which of the following statements about cycloaddition reactions is not true?

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Which of the following statements about thermal electrocyclic reactions is not true?

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Predict the major organic product(s) of the following electrocyclic reaction.

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Which of the following statements about photochemical electrocyclic reactions is not true?

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What is the correct classification of the following reaction?

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Consider the following reaction sequence.What is the correct classification of the first reaction in the sequence?

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Which of the following statements about an electrocyclic ring-opening reaction is not true?

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Which of the following statements about pericyclic reactions is not true?

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Which of the following statements about a p-bonding molecular orbital is true?

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Predict the major organic product(s) of the following electrocyclic reaction.

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What are the two modes of bond formation in cycloaddition reactions?

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Which of the following statements about sigmatropic reactions is not true?

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Predict the major organic product(s) of the following electrocyclic reaction.

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Consider the following reaction sequence.What is the correct classification of the second reaction in the sequence?

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What type of sigmatropic rearrangement is illustrated below?

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