Question 1

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 pbonds. 
C) Photochemical electrocyclic reactions occur in a disrotatory fashion for a conjugated polyene with an even number of pbonds. 
D) In photochemical reactions, we consider the orbitals of the LUMO of the excited state to determine the course of the reaction. 
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 pbonds. 
C) Photochemical electrocyclic reactions occur in a disrotatory fashion for a conjugated polyene with an even number of pbonds. 
D) In photochemical reactions, we consider the orbitals of the LUMO of the excited state to determine the course of the reaction.

Question 2

Which of the following statements about electrocyclic ring closure is not true?

Accepted Answer

A) It is an intramolecular reaction. 
B) It requires heat or light. 
C) The cyclic product contains one more s bond and one fewer p bond than the reactants. 
D) The cyclic product contains one more p bond and one fewer s bond than the reactants. 
A) It is an intramolecular reaction. 
B) It requires heat or light. 
C) The cyclic product contains one more s bond and one fewer p bond than the reactants. 
D) The cyclic product contains one more p bond and one fewer s bond than the reactants.

Question 3

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

Question 4

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

Question 5

Which of the following statements about electrocyclic reactions is true?

Accepted Answer

A) An electrocyclic reaction is generally irreversible. 
B) Generally, an acyclic triene is favored over a six-membered ring at equilibrium. 
C) Generally, a four-membered ring is favored over an acyclic diene at equilibrium. 
D) An electrocyclic reaction is generally reversible. 
A) An electrocyclic reaction is generally irreversible. 
B) Generally, an acyclic triene is favored over a six-membered ring at equilibrium. 
C) Generally, a four-membered ring is favored over an acyclic diene at equilibrium. 
D) An electrocyclic reaction is generally reversible.

Question 6

What type of sigmatropic rearrangement is illustrated below?

Accepted Answer

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

Question 7

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] Cycloaddition 
A) [2 + 2] Cycloaddition 
B) [6 + 4] Cycloaddition 
C) [4 + 4] Cycloaddition 
D) [4 + 2] Cycloaddition

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 p electrons in the two products. 
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.

Question 9

Which of the following statements about sigmatropic rearrangements and orbital symmetry is not true?

Accepted Answer

A) Reactions involving six atoms or fewer must take place by suprafacial pathways. 
B) In a suprafacial rearrangement, the new sbond forms on the opposite side of the psystem as the broken s bond. 
C) In an antarafacial rearrangement, the new sbond forms on the opposite side of the psystem as the broken s bond. 
D) In a suprafacial rearrangement, the new sbond forms on the same side of the p system as the broken s bond. 
A) Reactions involving six atoms or fewer must take place by suprafacial pathways. 
B) In a suprafacial rearrangement, the new sbond forms on the opposite side of the psystem as the broken s bond. 
C) In an antarafacial rearrangement, the new sbond forms on the opposite side of the psystem as the broken s bond. 
D) In a suprafacial rearrangement, the new sbond forms on the same side of the p system as the broken s bond.

Question 10

How many p molecular orbitals are present in 1,3,5,7,9-decapentaene?

Accepted Answer

A) 4 
B) 5 
C) 10 
D) 12 
A) 4 
B) 5 
C) 10 
D) 12

Question 11

Which of the following is not a correct designation for a sigmatropic rearrangement?

Accepted Answer

A) [1,3] 
B) [1,5] 
C) [3,3] 
D) [3,1] 
A) [1,3] 
B) [1,5] 
C) [3,3] 
D) [3,1]

Question 12

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

Accepted Answer

A) 3 
B) 4 
C) 5 
D) 6 
A) 3 
B) 4 
C) 5 
D) 6

Question 13

How many bonding molecular orbitals are present in 1,3,5,7,9-decapentaene?

Accepted Answer

A) 4 
B) 5 
C) 10 
D) 12 
A) 4 
B) 5 
C) 10 
D) 12

Question 14

Which of the following statements about pericyclic reactions is true?

Accepted Answer

A) Pericyclic reactions occur by way of ionic intermediates. 
B) Pericyclic reactions occur by way of radical intermediates. 
C) Pericyclic reactions involve multiple steps. 
D) Reactive intermediates are not formed in pericyclic reactions. 
A) Pericyclic reactions occur by way of ionic intermediates. 
B) Pericyclic reactions occur by way of radical intermediates. 
C) Pericyclic reactions involve multiple steps. 
D) Reactive intermediates are not formed in pericyclic reactions.

Question 15

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] 
A) [2+2] 
B) [4+2] 
C) [4+4] 
D) [0+2]

Question 16

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. 
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.

Question 17

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. 
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.

Question 18

Which of the following is a type of pericyclic reaction?

Accepted Answer

A) electrocyclic reactions 
B) acyclic reactions 
C) cycloelimination reactions 
D) electrophilic reactions 
A) electrocyclic reactions 
B) acyclic reactions 
C) cycloelimination reactions 
D) electrophilic reactions

Question 19

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

Accepted Answer

A) I 
B) II 
C) III 
D) IV 
A) I 
B) II 
C) III 
D) IV

Question 20

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. 
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.

Exam 27: Pericyclic Reactions

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

Which of the following statements about electrocyclic ring closure is not true?

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

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

Which of the following statements about electrocyclic reactions is true?

What type of sigmatropic rearrangement is illustrated below?

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

Which of the following statements about cycloaddition reactions is true?

Which of the following statements about sigmatropic rearrangements and orbital symmetry is not true?

How many p molecular orbitals are present in 1,3,5,7,9-decapentaene?

Which of the following is not a correct designation for a sigmatropic rearrangement?

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

How many bonding molecular orbitals are present in 1,3,5,7,9-decapentaene?

Which of the following statements about pericyclic reactions is true?

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

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

Which of the following statements about molecular orbitals is true?

Which of the following is a type of pericyclic reaction?

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

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

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Understanding Organic Reactions

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Carboxylic Acids and the Acidity of the O-H Bond

Introduction to Carbonyl Chemistry;

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Substitution Reactions of Carbonyl Compounds at the Alpha-Carbon

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Carbon-Carbon Bond Forming Reactions in Organic Synthesis

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