TRB PG Assistant - Pericyclic reactions, electrocyclisation, cycloaddition and sigmatropic rearrangements Online Test (MCQ Quiz)

1. Which type of pericyclic reaction involves the formation of a new cyclic system from two or more unsaturated molecules?

A) Electrocyclisation B) Cycloaddition C) Sigmatropic rearrangement D) Cheletropic reaction

2. In a [4+2] cycloaddition reaction, how many pi electrons are involved in the transition state?

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

3. Which of the following is a characteristic feature of pericyclic reactions?

A) Radical intermediates B) Concerted mechanism C) Stepwise mechanism D) Ionic intermediates

4. The Woodward-Hoffmann rules predict the stereochemistry of pericyclic reactions based on which principle?

A) Orbital symmetry B) Steric hindrance C) Electronic effects D) Thermodynamic stability

5. What is the minimum number of atoms that must rearrange in a sigmatropic rearrangement?

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

6. A [1,5]-sigmatropic rearrangement involves the migration of a sigma bond and a pi bond across how many atoms?

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

7. Which type of electrocyclisation involves the formation of a three-membered ring from a conjugated system?

A) 2 pi electron system B) 4 pi electron system C) 6 pi electron system D) 8 pi electron system

8. Thermal electrocyclisation of a 4 pi electron system typically results in the formation of a ring with how many members?

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

9. Photochemical electrocyclisation of a 4 pi electron system typically results in the formation of a ring with how many members?

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

10. The Diels-Alder reaction is a classic example of which type of pericyclic reaction?

A) Electrocyclisation B) Sigmatropic rearrangement C) [4+2] Cycloaddition D) [2+2] Cycloaddition

11. In a [2+2] cycloaddition reaction, what is the typical stereochemical outcome under thermal conditions?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

12. Which of the following is a requirement for a concerted mechanism in pericyclic reactions?

A) Presence of a solvent B) High temperature C) Continuous overlap of orbitals D) Radical initiator

13. According to the Woodward-Hoffmann rules, a thermal electrocyclisation of a 6 pi electron system proceeds via which motion?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

14. A [3,3]-sigmatropic rearrangement is also known as which reaction?

A) Cope rearrangement B) Claisen rearrangement C) Diels-Alder reaction D) Ene reaction

15. The Claisen rearrangement is a specific type of [3,3]-sigmatropic rearrangement involving which functional groups?

A) Alkenes and alkynes B) Allylic vinyl ethers C) Allylic alcohols D) Allylic halides

16. Which term describes the movement of a sigma bond across a pi system in a sigmatropic rearrangement?

A) Migration B) Addition C) Elimination D) Rearrangement

17. Photochemical [2+2] cycloaddition reactions typically proceed via which motion?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

18. The Ene reaction is a type of pericyclic reaction that involves the transfer of a hydrogen atom and the formation of a new sigma bond. What is another key feature?

A) Formation of a new pi bond B) Formation of a new cyclic system C) Migration of a double bond D) Both A and C

19. Which of the following is NOT a pericyclic reaction?

A) Diels-Alder reaction B) Claisen rearrangement C) SN2 reaction D) Electrocyclisation

20. In a [4+2] cycloaddition, the diene is considered the '4 pi electron' component and the dienophile is the '2 pi electron' component. What is the total number of pi electrons in the transition state?

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

21. What is the characteristic motion for a thermal electrocyclisation of a 6 pi electron system according to the Woodward-Hoffmann rules?

A) Conrotatory opening and disrotatory closing B) Disrotatory opening and conrotatory closing C) Disrotatory opening and disrotatory closing D) Conrotatory opening and conrotatory closing

22. Which type of sigmatropic rearrangement involves the migration of a hydrogen atom?

A) [1,2]-sigmatropic rearrangement B) [1,3]-sigmatropic rearrangement C) [1,5]-sigmatropic rearrangement D) All of the above

23. The stereochemistry of photochemical reactions is often governed by excited states. For a photochemical electrocyclisation of a 4 pi electron system, which motion is favored?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

24. Which term describes the simultaneous formation and breaking of sigma and pi bonds in a pericyclic reaction?

A) Stepwise process B) Concerted process C) Radical chain reaction D) Ionic mechanism

25. In a [2+2] cycloaddition, the photochemical reaction typically favors which motion?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

26. What is the designation for a sigmatropic rearrangement where a substituent migrates across a pi system, and the sigma bond breaks and forms between atoms separated by 'n' atoms in the pi system?

A) [n+m] B) [n]sigmatropic C) [n,m]-sigmatropic D) [n+1]

27. The Moebius strip analogy is used to explain the orbital symmetry rules for which type of pericyclic reaction?

A) Electrocyclisation B) Cycloaddition C) Sigmatropic rearrangement D) Cheletropic reactions

28. Which of the following is a characteristic of the suprafacial approach in cycloaddition reactions?

A) Bond formation on opposite faces of the pi system B) Bond formation on the same face of the pi system C) Involves an antarafacial component D) Leads to stereochemical inversion

29. The thermal electrocyclisation of a 1,3,5-hexatriene (6 pi electrons) leads to the formation of which ring size?

A) 3-membered ring B) 4-membered ring C) 5-membered ring D) 6-membered ring

30. Which term describes the movement of atoms or groups across a pi system in a concerted manner?

A) Cycloaddition B) Sigmatropic rearrangement C) Electrocyclisation D) Cheletropic reaction

31. In a [4+2] cycloaddition, the diene must be able to adopt which conformation for the reaction to occur?

A) S-cis B) S-trans C) Chair D) Boat

32. Which of the following is an example of a [1,5]-sigmatropic rearrangement?

A) Cope rearrangement B) Claisen rearrangement C) Prototropic shift D) Ene reaction

33. The stereochemical outcome of a photochemical electrocyclisation of a 6 pi electron system is typically:

A) Conrotatory B) Disrotatory C) Suprafacial D) Antarafacial

34. Which type of pericyclic reaction involves the simultaneous formation of two new sigma bonds from a single molecule?

A) Cycloaddition B) Electrocyclisation C) Sigmatropic rearrangement D) Cheletropic reaction

35. What is the primary driving force for many pericyclic reactions?

A) Formation of strong ionic bonds B) Preservation of orbital symmetry C) Generation of radical intermediates D) High activation energy

36. In the context of cycloadditions, what does the term 'antarafacial' refer to?

A) Bond formation on the same face of both reacting components B) Bond formation on opposite faces of one reacting component C) Bond formation on opposite faces of both reacting components D) Bond formation on the same face of both reacting components

37. Which of the following is a thermal electrocyclisation that results in a 5-membered ring?

A) 4 pi electron system B) 6 pi electron system C) 8 pi electron system D) 2 pi electron system

38. The term 'homo-sigmatropic rearrangement' refers to a sigmatropic rearrangement where the migration occurs across how many atoms, including the migrating group?

A) 2 B) 3 C) 4 D) 5

39. Which of the following is a key feature of the Woodward-Hoffmann rules?

A) Predicts reaction rates B) Determines thermodynamic stability C) Relates the symmetry of molecular orbitals in the ground and excited states to the reaction pathway D) Explains radical mechanisms

40. In the Diels-Alder reaction, the regioselectivity is often explained by considering the interaction between the HOMO of one component and the LUMO of the other. Which is typically the HOMO/LUMO pairing?

A) HOMO(diene)/LUMO(dienophile) B) LUMO(diene)/HOMO(dienophile) C) HOMO(diene)/HOMO(dienophile) D) LUMO(diene)/LUMO(dienophile)

41. What is the minimum number of atoms required to form a cyclic system in an electrocyclisation reaction?

A) 2 B) 3 C) 4 D) 5

42. Which type of pericyclic reaction involves a 'two-atom' component adding to a 'four-atom' pi system?

A) [4+2] Cycloaddition B) [2+2] Cycloaddition C) Electrocyclisation D) Sigmatropic rearrangement

43. The photochemical [4+2] cycloaddition reaction typically proceeds via which motion?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

44. Which of the following is a characteristic of a [1,2]-sigmatropic rearrangement?

A) Migration of a sigma bond over 3 atoms B) Migration of a sigma bond over 5 atoms C) Migration of a sigma bond over 2 atoms D) Migration of a pi bond over 3 atoms

45. The Wessely-Moser rearrangement is an example of a sigmatropic rearrangement often seen in which class of compounds?

A) Alkenes B) Aromatic compounds C) Steroids D) Carbohydrates

46. According to the Woodward-Hoffmann rules, a photochemical electrocyclisation of a 4 pi electron system proceeds via which motion?

A) Disrotatory B) Conrotatory C) Suprafacial D) Antarafacial

47. Which of the following is a feature of cheletropic reactions?

A) Involves two separate molecules reacting B) Involves the addition of a two-atom component to a pi system C) Involves a single atom or group coordinating to a pi system D) Involves rearrangement of atoms within a molecule

48. Which term describes the face selectivity in a pericyclic reaction where both components react on the same face?

A) Antarafacial B) Suprafacial C) Disrotatory D) Conrotatory

49. The thermal opening of a cyclobutene (4 pi electron system) is an example of which type of pericyclic reaction?

A) Electrocyclisation B) Cycloaddition C) Sigmatropic rearrangement D) Cheletropic reaction

50. Which of the following is a [2,3]-sigmatropic rearrangement?

A) Cope rearrangement B) Claisen rearrangement C) Wittig rearrangement D) Diels-Alder reaction

Pericyclic reactions, electrocyclisation, cycloaddition and sigmatropic rearrangements - Online Test

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