Deck 23: Special Topic: Reactions Controlled by Orbital Symmetry

Question 1

The starting compound undergoes a sigmatropic rearrangement to give the product shown.Which of these terms correctly describes the process that occurred?

A) 1,3 sigmatropic rearrangement
B) 1,5 sigmatropic rearrangement
C) 2,3 sigmatropic rearrangement
D) 3,3 sigmatropic rearrangement
E) None of these terms describes the process that occurred.

Answer 1

1,5 sigmatropic rearrangement

Question 2

What is the product of the thermal ring-opening electrocyclic reaction of cis-3,4-dimethylcyclobutene?

A) predominantly I
B) predominantly II
C) predominantly III
D) mixture of I and II in approximately equal amounts
E) mixture of II and III in approximately equal amounts

Answer 2

predominantly III

Question 3

Which of these electrocyclic reactions will occur through a disrotatory process?

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

Answer 3

I and IV

Question 4

What is the product of a [1,3] -sigmatropic shift in the following compound?

A)
B)
C) The compound shown cannot undergo a [1,3]-sigmatropic shift.
D)
E)

Question 5

Which of the following statements best describes the chemical events leading from starting material to product?

A) a [3,3] sigmatropic rearrangement, then an intramolecular Diels-Alder reaction
B) a [1,5] hydrogen shift/sigmatropic rearrangement, followed by a [3,3] sigmatropic rearrangement
C) two successive Diels-Alder reactions
D) two successive [3,3] sigmatropic rearrangements
E) an intramolecular Diels-Alder reaction followed by a [2,3] sigmatropic rearrangement

Question 6

Which statement is true regarding the favored process in this thermal electrocyclic reaction?

A)Conrotatory ring closure produces a racemic mixture.
B)Disrotatory ring closure produces a racemic mixture.
C)Conrotatory ring closure produces a single achiral product.
D)Disrotatory ring closure produces a single achiral product.
E)both a and c

Question 7

Consider the cycloaddition reaction below.Fill in the blanks: this reaction is ________ and is ________allowed

A) [6+4] ; thermally
B) [6+4] ; photochemically
C) [4+4] ; thermally
D) [4+4] ; photochemically
E) [4+2] ; thermally

Question 8

Which type of sigmatropic rearrangement is involved in this process?

A) 1,3
B) 1,5
C) 1,7
D) 2,2
E) 4,2

Question 9

What is the product of the thermal ring-closing electrocyclic reaction of (E,E) isomer of hexa-2,4-diene ?

A) I
B) II
C) III
D) mixture of I and II in equal amounts
E) mixture of II and III in equal amounts

Question 10

Which type of sigmatropic rearrangement is involved in this process?

A) 1,3
B) 1,5
C) 1,7
D) 2,2
E) 2,3

Question 11

Which type of sigmatropic rearrangement is involved in this process?

A) 1,3
B) 1,5
C) 1,7
D) 2,3
E) 3,3

Question 12

What is the product of the following photochemical [2+2] cycloaddition reaction? (OAc is acetoxy group

A)
B)
C)
D)
E)

Question 13

Which of these processes are thermally allowed?

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

Question 14

Which of these is the "thermal" HOMO for penta-2,4-dien-1-yl radical,

A)
B)
C)
D)
E)

Question 15

which of these is the "photochemical" номо for ally radical?

A)
B)
C)
D)
E)

Question 16

Which of these is the "photochemical" номо for buta-1,-3-diene?

A)
B)
C)
D)
E)

Question 17

Which of these is the "thermal" номо for allyl radical?

A)
B)
C)
D)
E)

Question 18

Which of these is the "thermal" номо for hexa-1,3,5-triene?

A)
B)
C)
D)
E)

Question 19

In which of the following systems will an antarafacial shift be impossible?

A)
B)
C)
D)
E) None of these systems can undergo an antarafacial shift.

Question 20

Which of these structures is the product of [3,3] sigmatropic rearrangement of this compound?

A)
B)
C)
D)
E) The compound shown cannot undergo a [3,3] sigmatropic rearrangement.

Question 21

Which of these structures is the product of Cope rearrangement of this compound?

A)
B)
C)
D)
E) None of these is the product of Cope rearrangement of the compound shown.

Question 22

What is a major isolated product arising from Cope (Claisen) rearrangement for the following compound?

A)
B)
C) This compound does not undergo such rearrangement.
D)
E)

Question 23

Rationalize why only the exo product is formed in the following [6+4] cycloaddition reaction.

Question 24

Draw the ground-state ("thermal") -molecular orbitals for the allyl radical and show electron occupancy on the corresponding energy diagram. Label HOMO and LUMO.

Question 25

Antarafacial [1,5] -hydride shifts are very rare, and then only occur in cyclic systems, such as the one shown below. What are the reaction conditions required?

Question 26

Draw the products of the electrocyclic reaction that would occur on heating this compound.

Question 27

Which of these structures does not undergo Cope rearrangement?

A)

B)

C)

D)

E)
All these compounds can undergo Cope rearrangement.

Question 28

Is the process shown conrotatory or disrotatory?

Question 29

Is this reaction allowed thermally or photochemically?

Question 30

Draw the -molecular orbitals for buta-1,3-diene and show electron occupancy on the corresponding energy diagram. Label "thermal" HOMO and "photochemical" HOMO.

Question 31

Ketene ' can dimerize in a [2+2] fashion using the bond of one molecule and the bond of another molecule. Draw the product of this cycloaddition.

Question 32

Draw the ground state ("thermal") and or excited state ("photochemical") highest-occupied -molecular orbitals (HOMOs) for octa-1,3,5,7-tetraene.

Question 33

Is the product shown the result of conrotation or disrotation?

Question 34

Explain why thermal dimerization of ethylene is symmetry forbidden.

Question 35

One of the monomers that makes up the DNA polymer is thymine.

Question 36

Draw the product of the conrotatory ring-closing electrocyclic reaction below.

Question 37

Is the product shown the result of suprafacial or antarafacial reaction?

Question 38

The following reaction is a sigmatropic shift. Provide the arrow formalism and determine the nature [x, y] of the shift.

Question 39

The thermal Diels-Alder reaction can occur through the interaction of the HOMO of the diene and the LUMO of the dienophile. Can the reaction also occur through the interaction of the HOMO of the dienophile and the LUMO of the diene? Using 1,3-butadiene and ethylene as your model system, provide orbital diagrams to support your answer.

Question 40

The following reaction involves a sigmatropic shift and another transformation you already know.
Provide arrow formalism for the sigmatropic shift and determine the nature of both steps.

Question 41

Draw the product of thermal Cope rearrangement of this compound.

Question 42

When both ortho positions on the aromatic ring are blocked, the enolization of the Claisen
rearrangement product is impossible.In this case two sequential [3,3]-shifts occur, affording a
trisubstituted phenol.Starting from the following allyl aryl ether, draw the arrow formalism for
both [3,3] shifts, showing the intermediates and the final product.

Question 43

Draw the isolated product arising from thermal Cope rearrangement of this compound.

Question 44

Predict the product of Claisen rearrangement of this compound.

Question 45

Draw the product of a [2,3]-sigmatropic shift reaction of the compound below.

Question 46

Draw the product of a [2,3] sigmatropic rearrangement of this compound.