Quiz Competition On Pericyclic Reactions

1. Which of the following dienes cannot undergo Diels-Alder reactions?

Option 1

Option 2

Option 3

Option 4

A diene has to be able to assume an s-cis conformation in order to undergo Diels-Alder reactions, and (d) has a constrained s-trans structure

Explanation

A diene has to be able to assume an s-cis conformation in order to undergo Diels-Alder reactions, and (d) has a constrained s-trans structure

2. Which of adducts (a)-(d) is the main product of the following Diels-Alder reaction?

Option 1

Option 2

Option 3

Option 4

The relative configurations of the diene and dienophile are preserved in the concerted syn addition of a Diels-Alder reaction. For the stereochemistry of Diels-Alder reactions

Explanation

The relative configurations of the diene and dienophile are preserved in the concerted syn addition of a Diels-Alder reaction. For the stereochemistry of Diels-Alder reactions

3. Which of the following dienophiles is the most reactive with buta-1,3-diene?

Option 1

Option 2

Option 3

Option 4

Compound (c) is the dienophile with the best combination of low steric hindrance and a low-energy LUMO (which is caused by the electron-withdrawing anhydride residue)

Explanation

Compound (c) is the dienophile with the best combination of low steric hindrance and a low-energy LUMO (which is caused by the electron-withdrawing anhydride residue)

4. Which of phenols (a)-(d) is the main product of the following thermal rearrangement?

Option 1

Option 2

Option 3

Option 4

The reaction is a Claisen rearrangement which is a type of [3,3] sigmatropic rearrangement

Explanation

The reaction is a Claisen rearrangement which is a type of [3,3] sigmatropic rearrangement

5. Which of the following reactions is not thermally allowed?

Option 1

Option 2

Option 3

Option 4

For some orbital symmetry controlled reactions, see pp. 478-5. Reaction (a) is a [2+2] cycloaddition, (b) a [3,3] sigmatropic rearrangement, (c) an electrocyclic reaction, and (d) an ene reaction.

Explanation

For some orbital symmetry controlled reactions, see pp. 478-5. Reaction (a) is a [2+2] cycloaddition, (b) a [3,3] sigmatropic rearrangement, (c) an electrocyclic reaction, and (d) an ene reaction.

6. The following involves two pericyclic reactions. Which combination indicates correctly the types of reaction involved?

[4+2] cycloaddition + [2+2] cycloreversion

Cheletropic reaction + [4+2] cycloaddition

[4+2] cycloaddition + [4+1] cycloreversion

[4+2] cycloaddition + cheletropic reaction

Carbon monoxide is lost from the intermediate adduct

Explanation

Carbon monoxide is lost from the intermediate adduct

7. Which of the following reactions is classified as an ene reaction?

Option 1

Option 2

Option 3

Option 4

Reactions (a) and (b) are both [3,3] sigmatropic rearrangements, (c) an electrocyclic reaction, and (d) an ene reaction.

Explanation

Reactions (a) and (b) are both [3,3] sigmatropic rearrangements, (c) an electrocyclic reaction, and (d) an ene reaction.

8. Which of the following is the main product in the ozonolysis of 1,4-dimethylcyclohexene followed by a reductive workup with Zn and ethanoic acid?

Option 1

Option 2

Option 3

Option 4

The products of ozonolysis followed by a reductive workup are aldehyde(s) and/or ketone(s). Note the position of the methyl substituent in the ring-opened product. For ozonolysis of alkenes

Explanation

The products of ozonolysis followed by a reductive workup are aldehyde(s) and/or ketone(s). Note the position of the methyl substituent in the ring-opened product. For ozonolysis of alkenes

9. Which of the following is the main product in the ozonolysis of 1,5-dimethylcyclohexene followed by a workup with aqueous H₂O₂?

Option 1

Option 2

Option 3

Option 4

The products of ozonolysis followed by an oxidative workup are carboxylic acid(s) and/or ketone(s). Note that the position of the methyl substituent in the ring-opened product. For ozonolysis of alkenes

Explanation

The products of ozonolysis followed by an oxidative workup are carboxylic acid(s) and/or ketone(s). Note that the position of the methyl substituent in the ring-opened product. For ozonolysis of alkenes

10. Which of the following is classified as an electrocyclic reaction?

Option 1

Option 2

Option 3

Option 4

Electrocyclic reactions involve the cyclization of a conjugated polyene, where a pi bond is formed by the overlap of two p orbitals from adjacent atoms. This is exactly what happens in Option 1. The conjugated diene rearranges to form a cyclobutene ring with a new sigma bond between the two carbons that were originally part of the double bonds.

Explanation

Electrocyclic reactions involve the cyclization of a conjugated polyene, where a pi bond is formed by the overlap of two p orbitals from adjacent atoms. This is exactly what happens in Option 1. The conjugated diene rearranges to form a cyclobutene ring with a new sigma bond between the two carbons that were originally part of the double bonds.