Question 1

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

Accepted Answer

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

Question 2

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.

Accepted Answer

A  [5,5] -sigmatropic shift, followed by enolization of the intermediate ketone.

Question 3

Which type of sigmatropic rearrangement is involved in this process?

Accepted Answer

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

Question 4

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

Accepted Answer

A)    
B)    
C)    
D)    
E)    
A)    
B)    
C)    
D)    
E)

Question 5

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

Accepted Answer

The answer of Draw the isolated product arising from thermal...

Question 6

Is this reaction allowed thermally or photochemically?

Accepted Answer

It is a disrotatory ring-closi

Question 7

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

Accepted Answer

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 
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

Question 8

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

Accepted Answer

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. 
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.

Question 9

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

Accepted Answer

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

Question 10

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

Accepted Answer

The answer of Draw the ground-state ("thermal")  -molecular orbitals...

Question 11

Predict the product of Claisen rearrangement of this compound.

Accepted Answer

The answer of Predict the product of Claisen rearrangement of...

Question 12

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

Accepted Answer

The answer of Draw the products of the electrocyclic reaction...

Question 13

Which of these structures does not undergo Cope rearrangement?

Accepted Answer

A) 
  
B) 
  
C) 
  
D) 
  
E) 
 All these compounds can undergo Cope rearrangement. 
A) 
  
B) 
  
C) 
  
D) 
  
E) 
 All these compounds can undergo Cope rearrangement.

Question 14

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

Accepted Answer

The answer of One of the monomers that makes up...

Question 15

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.

Accepted Answer

The answer of When both ortho positions on the aromatic...

Question 16

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

Accepted Answer

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 
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 17

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?

Accepted Answer

More common suprafacial  [1,5] -hydride

Question 18

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

Accepted Answer

A)  I 
B)  II 
C)  III 
D)  mixture of I and II in equal amounts 
E)  mixture of II and III in equal amounts 
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 19

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.

Accepted Answer

When the HOMO of the dienophile and the

Question 20

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

Accepted Answer

Exo and endo transition states can be co

Exam 23: Special Topic: Reactions Controlled by Orbital Symmetry

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

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.

Which type of sigmatropic rearrangement is involved in this process?

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

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

Is this reaction allowed thermally or photochemically?

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

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

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

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

Predict the product of Claisen rearrangement of this compound.

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

Which of these structures does not undergo Cope rearrangement?

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

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

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?

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

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

Atoms and Molecules; Orbitals and Bonding

Alkanes

Alkenes and Alkynes

Stereochemistry

Rings

Substituted Alkanes: Alkyl Halides, Alcohols, Amines, Ethers,thiols, and Thioethers

Substitution Reactions: the Sn2 and Sn1 Reactions

Elimination Reactions: the E1 and E2 Reactions

Analytical Chemistry: Spectroscopy

Electrophilic Additions to Alkenes

More Additions to Bonds

Radical Reactions

Dienes and the Allyl System: 2p Orbitals in Conjugation

Aromaticity

Substitution Reactions of Aromatic Compounds

Carbonyl Chemistry 1: Addition Reactions

Carboxylic Acids

Derivatives of Carboxylic Acids: Acyl Compounds

Carbonyl Chemistry 2: Reactions at the Α Position

Special Topic: Carbohydrates

Special Topic: Bio-Organic Chemistry

Special Topic: Amino Acids and Polyamino Acids Peptides and Proteins

Special Topic: Intramolecular Reactions and Neighboring Group Participation

Filters