Question 1

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,  bond is broken in one of the reactants.
C)   The  bonds rearrange in a sigmatropic reaction.
D)   The number of  bonds in the reactants and product differs in a sigmatropic reaction.E) B) and C)
F) All of the above

Question 2

Why is the Diels-Alder reaction called a thermal [4+2] cycloaddition?

Accepted Answer

A)   Because the reaction is initiated by heat; the diene has four  electrons and the dienophile has two  electrons.
B)   Because the reaction is initiated by light; the diene has four  electrons and the dienophile has two  electrons.
C)   Because the reaction is initiated by heat; the dienophile has four  electrons and the diene has two  electrons.
D)   Because the reaction is initiated by light; the dienophile has four  electrons and the diene has two  electrons.E) A) and B)
F) A) and D)

Question 3

What type of sigmatropic rearrangement is illustrated below?

Accepted Answer

A)   [1,3]
B)   [1,4]
C)   [3,3]
D)   [1,5]E) A) and D)
F) A) and C)

Question 4

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

Accepted Answer

A)   The number of  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  bonds.
C)   Thermal electrocyclic reactions occur in a conrotatory fashion for a conjugated polyene with an even number of  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) A) and B)
F) A) and C)

Question 5

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

Accepted Answer

A)   Thermal cycloadditions involving an even number of  bonds proceed by a suprafacial pathway.
B)   Thermal cycloaddition involving an odd number of  bonds proceed by an antarafacial pathway.
C)   Photochemical cycloadditions involving an even number of  bonds proceed by an antarafacial pathway.
D)   Photochemical cycloadditions involving an even number of  bonds proceed by a suprafacial pathway.E) None of the above
F) C) and D)

Question 6

How many  molecular orbitals are present in 1,3,5-hexatriene?

Accepted Answer

A)   3
B)   4
C)   5
D)   6E) All of the above
F) C) and D)

Question 7

Which of the following statements about  orbitals is true?

Accepted Answer

A)   " orbitals are formed by the linear combination of two sp3 orbitals."
B)   " orbitals are formed by the linear combination of two sp2 orbitals."
C)   " orbitals are formed by the linear combination of two sp orbitals."
D)   " orbitals are formed by the linear combination of two p orbitals."E) A) and B)
F) All of the above D

Question 8

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  electrons in the two products.E) B) and D)
F) A) and B)

Question 9

What type of cycloaddition reaction is shown in the following equation?

Accepted Answer

A)   [2+2]
B)   [4+2]
C)   [4+4]
D)   [0+2]E) All of the above
F) None of the above

Question 10

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

Accepted Answer

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

Question 11

Which of the following is not a type of pericyclic reactions?

Accepted Answer

A)   cycloadditions
B)   nucleophilic reactions
C)   electrocyclic reactions
D)   sigmatropic rearrangementsE) A) and D)
F) B) and C)

Question 12

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

Accepted Answer

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

Question 13

Which of the following statements about molecular orbitals is true?

Accepted Answer

A)   The number of molecular orbitals formed is different from the number of atomic orbitals used.
B)   The number of molecular orbitals formed is equal to the number of atomic orbitals used.
C)   The number of molecular orbitals formed is equal to twice the number of atomic orbitals used.
D)   The number of molecular orbitals formed is equal to half the number of atomic orbitals used.E) C) and D)
F) A) and C)

Question 14

What is the correct classification of the following reaction?

Accepted Answer

A)   cycloaddition reaction
B)   electrophilic reaction
C)   electrocyclic reaction
D)   sigmatropic reactionE) B) and C)
F) None of the above

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) None of the above B

Question 16

Which of the following statements about sigmatropic reactions is true?

Accepted Answer

A)   The reactants contain one more  bond than the product.
B)   The product contains one more  bond than the reactant.
C)   A  bond is broken in the reactant.
D)   A  bond is broken in the reactant.E) A) and B)
F) A) and C)

Question 17

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 18

What is the correct classification of the following reaction?

Accepted Answer

A)   cycloaddition reaction
B)   electrocyclic reaction
C)   electrophilic reaction
D)   sigmatropic reactionE) A) and C)
F) B) and C)

Question 19

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

Accepted Answer

A)   Thermal cycloadditions involving an even number of  bonds proceed by a suprafacial pathway.
B)   Thermal cycloadditions involving an odd number of  bonds proceed by a suprafacial pathway.
C)   Photochemical cycloadditions involving an odd number of  bonds proceed by a suprafacial pathway.
D)   Photochemical sycloadditions involving an even number of  bonds proceed by an antarafacial pathway.E) None of the above
F) All of the above

Question 20

Which of the following is a type of pericyclic reaction?

Accepted Answer

A)   electrocyclic reactions
B)   acyclic reactions
C)   cycloelimination reactions
D)   electrophilic reactionsE) C) and D)
F) All of the above

Exam 27: Pericyclic Reactions

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

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Why is the Diels-Alder reaction called a thermal [4+2] cycloaddition?

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What type of sigmatropic rearrangement is illustrated below?

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

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

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How many  molecular orbitals are present in 1,3,5-hexatriene?

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Which of the following statements about  orbitals is true?

Correct AnswerverifiedD

Which of the following statements about cycloaddition reactions is true?

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What type of cycloaddition reaction is shown in the following equation?

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

Correct AnswerverifiedB

Which of the following is not a type of pericyclic reactions?

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

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Which of the following statements about molecular orbitals is true?

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What is the correct classification of the following reaction?

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

Correct AnswerverifiedB

Which of the following statements about sigmatropic reactions is true?

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What is the correct classification of the following reaction?

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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 is a type of pericyclic reaction?

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D

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B

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B

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