Deck 28: Pericyclic Reactions

Question 1

In the allyl radical,which π molecular orbital is singly occupied?

A)the bonding π molecular orbital
B)the nonbonding π molecular orbital
C)the antibonding π molecular orbital
D)none of the above

Answer 1

the nonbonding π molecular orbital

Question 2

Which of the following reactions best describes the Diels-Alder reaction?

A)electrocyclic reaction
B)cycloaddition reaction
C)sigmatropic reaction
D)radical reaction
E)nucleophilic substitution reaction

Answer 2

cycloaddition reaction

Question 3

Which of the following statements best describes the theory of Conservation of Orbital Symmetry?

A)Molecular orbital of the transition state must be similar to that of the reactant.
B)Molecular orbital of the transition state must be similar to that of the product.
C)Only s orbitals from reactants and products are utilized.
D)Molecular orbitals of reactant and product must have similar symmetry.
E)Molecular orbitals of reactant and product must have different symmetry.

Answer 3

Molecular orbitals of reactant and product must have similar symmetry.

Question 4

Which of the following molecular orbitals are formed from subtractive overlap of atomic orbitals?

A)antibonding orbitals
B)out-of-phase orbitals
C)bonding orbitals
D)A and B
E)B and C

Question 5

Describe an electrocyclic reaction.

A)The reactant has lost a sigma bond,the product has a new sigma bond,and the pi bonds have rearranged.
B)The product contains a new ring,with two less sigma bonds,and two more pi bonds than the starting material.
C)The product contains a new ring,with two more sigma bonds,and two less pi bonds than the starting material.
D)The product contains a new ring,with one less sigma bond,and one more pi bond than the starting material.
E)The product contains a new ring,with one more sigma bond,and one less pi bond than the starting material.

Question 6

How many nodes does the highest energy molecular orbital of 1,3,5,7-octatetraene have?

A)4
B)5
C)6
D)8
E)10

Question 7

Which of the following sets of atomic orbitals form an asymmetric molecular orbital?

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

Question 8

Describe a cycloaddition reaction.

A)The reactant has lost a sigma bond,the product has a new sigma bond,and the pi bonds have rearranged.
B)The product contains a new ring,with two less sigma bonds,and two more pi bonds than the starting material.
C)The product contains a new ring,with two more sigma bonds,and two less pi bonds than the starting material.
D)The product contains a new ring,with one less sigma bond,and one more pi bond than the starting material.
E)The product contains a new ring,with one more sigma bond,and one less pi bond than the starting material.

Question 9

What is meant by frontier orbitals?

Question 10

Describe a sigmatropic rearrangement.

A)A sigma bond in the reactant has moved to a different location in the product,and the pi bonds have rearranged.
B)The product contains a new ring,with two less sigma bonds,and two more pi bonds than the starting material.
C)The product contains a new ring,with two more sigma bonds,and two less pi bonds than the starting material.
D)The product contains a new ring,with one less sigma bond,and one more pi bond than the starting material.
E)The product contains a new ring,with one more sigma bond,and one less pi bond than the starting material.

Question 11

What are the three most common pericyclic reactions? Give examples.

Question 12

How many π molecular orbitals does 1,3,5,7-octatetraene have?

A)2
B)4
C)6
D)8
E)10

Question 13

What does LCAO stand for?

Question 14

Which of the following statements concerning the selection rules for pericyclic reactions is correct?

A)If TE describes the reaction,then the outcome is given by AC.
B)If PO describes the reaction,then the outcome is given by AC.
C)If TO describes the reaction,then the outcome is given by AC.
D)both A and B
E)none of the above

Question 15

Which of the following molecular orbitals is produced when in-phase atomic orbitals overlap?

A)a bonding molecular orbital
B)an antibonding molecular orbital
C)a nonbonding molecular orbital
D)an out-of-phase molecular orbital
E)an excited energy state of molecular orbital

Question 16

Through what type of single pericyclic reaction did the reaction shown below proceed?

A)[1,2] sigmatropic hydrogen migration
B)[1,3] sigmatropic hydrogen migration
C)[1,4] sigmatropic hydrogen migration
D)[1,5] sigmatropic hydrogen migration
E)none of the above

Question 17

How many molecular orbitals are produced from the overlap of four p atomic orbitals?

A)2
B)8
C)4
D)16
E)1

Question 18

Show the mechanism for each of the following pericyclic reactions.

Question 19

How many electrons are present in the nonbonding π molecular orbital of the allyl anion?

A)0
B)1
C)2
D)3
E)4

Question 20

Indicate whether each of the following reactions is an electrocyclic reaction,a cycloaddition reaction,or a sigmatropic rearrangement.

Question 21

Under thermal conditions,(2E,4Z)-hexadiene undergoes a ________ ring closure to yield ________.

A)conrotatory,cis-3,4-dimethylcyclobutene
B)conrotatory,trans-3,4-dimethylcyclobutene
C)disrotatory,cis-3,4-dimethylcyclobutene
D)disrotatory,trans-3,4-dimethylcyclobutene

Question 22

Under thermal conditions,(2E,4E)-hexadiene undergoes a ________ ring closure to yield ________.

A)conrotatory,cis-3,4-dimethylcyclobutene
B)conrotatory,trans-3,4-dimethylcyclobutene
C)disrotatory,cis-3,4-dimethylcyclobutene
D)disrotatory,trans-3,4-dimethylcyclobutene

Question 23

Give the product(s)for the following reaction.

A)
B)
C)
D)
E)

Question 24

What is the major product of the following reaction?

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

Question 25

Give the product(s)for the following reaction.You may choose more than one answer.

A)
B)
C)
D)
E)

Question 26

Which molecular orbital is higher in energy: the in-phase or out-of-phase overlap of atomic orbitals?

Question 27

(a)Under thermal conditions,will ring closure of (2E,4Z,6Z,8E)-decatetraene be conrotatory or disrotatory? Explain.
(b)Will the product be cis or trans? Explain

Question 28

How many nodes would you expect from the following atomic orbital overlap?

Question 29

Which of the following statements about the product of the electrocyclic ring closure below is correct?

A)The methyl groups are trans in the product.
B)The product arose from a stereospecific,conrotatory ring closure.
C)The product mixture is optically active.
D)both B and C
E)all of the above

Question 30

Explain what a node is and how it is formed.

Question 31

Which of the following statements concerning electrocyclic reactions is correct?

A)The ground state HOMO of a compound with an even number of conjugated double bonds is asymmetric.
B)The allowed mode of ring closure under thermal conditions for a molecule containing an even number of conjugated double bonds is disrotatory.
C)The allowed mode of ring closure under photochemical conditions for a molecule containing an odd number of conjugated double bonds is disrotatory.
D)both B and C
E)none of the above

Question 32

Under photochemical conditions,(2E,4Z)-hexadiene undergoes a ________ ring closure to yield ________.

A)conrotatory,cis-3,4-dimethylcyclobutene
B)conrotatory,trans-3,4-dimethylcyclobutene
C)disrotatory,cis-3,4-dimethylcyclobutene
D)disrotatory,trans-3,4-dimethylcyclobutene

Question 33

Give a representation of the bonding π molecular orbital of the allyl cation.

Question 34

Electrocyclic reactions are reversible.The cyclic compound is favored for electrocyclic reactions that form six-membered rings,whereas the open-chain compound is favored for reactions that form four-membered rings.Explain thoroughly in terms of the enthalpy changes that are occurring.

Question 35

Under photochemical conditions,(2E,4E)-hexadiene undergoes a ________ ring closure to yield ________.

A)conrotatory,cis-3,4-dimethylcyclobutene
B)conrotatory,trans-3,4-dimethylcyclobutene
C)disrotatory,cis-3,4-dimethylcyclobutene
D)disrotatory,trans-3,4-dimethylcyclobutene

Question 36

Give a representation of the antibonding π molecular orbital of the allyl anion.

Question 37

Draw the structure of the major organic product of the following reaction.Is the product chiral or achiral?

Question 38

Give the product(s)for the following reaction.You may choose more than one answer.

A)
B)
C)
D)
E)

Question 39

What is the major product of the following reaction?

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

Question 40

Consider the π molecular orbitals of pentadienyl cation and answer the following questions.Please refer to the lowest π MO as ψ₁.
a)How many π molecular orbitals of pentadienyl cation are bonding?
b)Which π molecular orbital is the HOMO?
c)Which π molecular orbitals are asymmetric with respect to a mirror plane perpendicular to the molecular plane?

Question 41

What is the major product of the following reaction?

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

Question 42

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 43

Consider the possible thermal [4+4] cycloaddition of two molecules of 1,3-butadiene to generate cycloocta-1,5-diene.Show the HOMO/LUMO interaction which would result,and use this interaction to predict whether the proposed cycloaddition could occur.

Question 44

Give the product for the following thermal reaction.

A)
B)
C)
D)
E)

Question 45

Which of the following statements best describes the term suprafacial?

A)formation of two sigma bonds from the same side of the pi system
B)formation of two pi bonds from the same side of the sigma system
C)formation of two sigma bonds from opposite sides of the pi system
D)formation of two pi bonds from opposite sides of the sigma system
E)an anti cycloaddition

Question 46

Explain why the following (2+2)cycloaddition reaction would work under photochemical conditions but not under thermal conditions.

Question 47

Is the thermal [4+2] cycloaddition between allylanion and ethylene an allowed one? To answer,draw the HOMO of allyl anion and the LUMO of ethylene,and comment on the symmetry match of the two.

Question 48

When an allyl anion undergoes a cycloaddition under thermal conditions with ethylene (bonds forming at the ends of the π-systems),the cycloaddition is described as

A)[2+2] and suprafacial.
B)[2+4] and suprafacial.
C)[2+2] and antarafacial.
D)[2+4] and antarafacial.
E)[2+3] and antarafacial.

Question 49

Under photochemical conditions,is an [2+2] cycloaddition suprafacial or antarafacial?

Question 50

Give the product for the following reaction.

A)
B)
C)
D)
E)no reaction

Question 51

Provide the structure of the major organic product in the following reaction.

Question 52

Why does the diene shown below fail to undergo a Diels-Alder reaction with even the most reactive dienophiles?

Question 53

Under thermal conditions,is an [8+2] cycloaddition suprafacial or antarafacial?

Question 54

What are the structures of A,B,and C?

Question 55

Give the product for the following reaction.

A)
B)
C)
D)
E)no reaction

Question 56

When an allyl cation undergoes a cycloaddition under photochemical conditions with ethylene (bonds forming at the ends of the π-systems),the cycloaddition is described as

A)[2+2] and suprafacial.
B)[2+4] and suprafacial.
C)[2+2] and antarafacial.
D)[2+4] and antarafacial.
E)[2+3] and antarafacial.

Question 57

What diene and dienophile would react to give the product below?

Question 58

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 59

Which of the following ring formations must involve a suprafacial bond formation?

A)four-membered ring
B)five-membered ring
C)six-membered ring
D)A and C
E)A,B and C

Question 60

Which of the following pericyclic reactions best describes the following reaction?

A)nucleophilic
B)electrocyclic
C)radical
D)sigmatropic
E)cycloaddition

Question 61

Under what conditions would a 1,3-hydrogen shift occur in a sigmatropic rearrangement?

A)thermal conditions
B)photochemical conditions
C)suprafacial pathway
D)A and C
E)B and C

Question 62

Provide the major organic product of the following Diels-Alder cycloaddition.

Question 63

What is the product of the following 1,5-hydrogen shift? CH₃CH CHCH CD₂ ?

A)CH₂ CHCH₂CH CHD
B)CH₂ CHCH CHCHD₂
C)CHD CHCH CHCH₃
D)CH₂ CHCH₂CH₂CH₂D
E)CH₂ CHCH CHCD₃

Question 64

What is the product from the following 1,3-carbon shift reaction?

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

Question 65

Which of the following best describes the sigmatropic rearrangement that occurs in the reaction shown below?

A)[1,3] sigmatropic rearrangement
B)[2,3] sigmatropic rearrangement
C)[3,3] sigmatropic rearrangement
D)[1,5] sigmatropic rearrangement
E)[1,4] sigmatropic rearrangement

Question 66

What is the major product from the following rearrangement?

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

Question 67

Which of the following statements about carbon migrations is correct?

A)Carbon migrations never occur by a sigmatropic rearrangement.
B)Under thermal conditions,a [1,3] carbon migration that occurs suprafacially must also occur with inversion of configuration at the migrating carbon.
C)Under thermal conditions,a [1,5] carbon migration that occurs suprafacially must also occur with inversion of configuration at the migrating carbon.
D)Under thermal conditions,a carbon migration that occurs suprafacially must occur with inversion no matter the system's symmetry.
E)B,C,and D

Question 68

Provide the major organic product of the following Diels-Alder cycloaddition.

Question 69

Which of the following best explains the rearrangement when provitamin D₃ rearranges to vitamin D₃?

A)[1,7] cycloaddition rearrangement,antarafacial
B)[1,7] cycloaddition rearrangement,suprafacial
C)[1,7] sigmatropic rearrangement,antarafacial
D)[1,7] sigmatropic rearrangement,suprafacial
E)[1,7] electrocyclic reaction,suprafacial

Question 70

What is the product of the following 1,7-hydrogen shift?

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

Question 71

Which of the following compounds is the most reactive dienophile in a Diels-Alder reaction with 1,3-butadiene?

A)CH₂ CHOCH₃
B)CH₂ CHCHO
C)CH₃CH CHCH₃
D)(CH₃)₂C CH₂
E)CH₂ CH₂

Question 72

Provide the major organic product of the following Diels-Alder cycloaddition.

Question 73

Under what conditions would a 1,5-hydrogen shift occur in a sigmatropic rearrangement?

A)thermal conditions
B)photochemical conditions
C)suprafacial pathway
D)A and C
E)B and C

Question 74

Provide the major organic product of the following Diels-Alder cycloaddition.

Question 75

What is the major product of the following [3,3] sigmatropic rearrangement?

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

Question 76

What type of pericyclic process is occurring in the reaction below? Provide two reasons why the equilibrium lies in the direction indicated.

Question 77

What is the product obtained from the following [1,5] sigmatropic rearrangement?

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

Question 78

Provide the major organic product of the following Diels-Alder cycloaddition.

Question 79

What is/are the product(s)of the following 1,3-hydrogen shift?

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

Question 80

Show the mechanism for the following 1,3-hydrogen shift.