TRB PG Assistant - Reactive intermediates: carbocations, carbanions, free radicals, carbenes and nitrenes Online Test (MCQ Quiz)

1. Which of the following is the most stable carbocation?

A) Methyl carbocation B) Ethyl carbocation C) Isopropyl carbocation D) tert-Butyl carbocation

2. Carbanions are typically formed by the abstraction of which type of hydrogen atom?

A) Acidic hydrogen B) Alkene hydrogen C) Alkyne hydrogen D) Hydroxyl hydrogen

3. Free radicals are characterized by the presence of:

A) A lone pair of electrons B) An unpaired electron C) A positive charge D) A negative charge

4. Carbenes are neutral molecules with a carbon atom having:

A) Two bonding electrons and a lone pair B) Two bonding electrons and an unpaired electron C) Three bonding electrons and a lone pair D) Three bonding electrons and an unpaired electron

5. Nitrenes are the nitrogen analogues of:

A) Carbocations B) Carbanions C) Carbenes D) Free radicals

6. The stability order of carbocations from least to most stable is:

A) tert-Butyl > Isopropyl > Ethyl > Methyl B) Methyl < Ethyl < Isopropyl < tert-Butyl C) Isopropyl < tert-Butyl < Methyl < Ethyl D) Ethyl < Methyl < tert-Butyl < Isopropyl

7. Which of the following is an example of a carbanion?

A) CH3+ B) CH3- C) CH3. D) CH2

8. Homolytic cleavage of a covalent bond leads to the formation of:

A) Carbocations B) Carbanions C) Free radicals D) Carbenes

9. Singlet carbenes have their two non-bonding electrons in:

A) Two different orbitals with opposite spins B) The same orbital with opposite spins C) Two different orbitals with parallel spins D) The same orbital with parallel spins

10. Which of the following is a common method for generating free radicals?

A) Reaction with strong bases B) Reaction with strong acids C) Homolysis induced by heat or light D) Nucleophilic substitution

11. The hybridization of the carbon atom in a methyl carbocation (CH3+) is:

A) sp3 B) sp2 C) sp D) s

12. Which species is resonance stabilized?

A) tert-Butyl carbocation B) Allyl carbocation C) Methyl carbocation D) Isopropyl carbocation

13. The stability of carbanions follows the order:

A) tert-Butyl < Isopropyl < Ethyl < Methyl B) Methyl < Ethyl < Isopropyl < tert-Butyl C) tert-Butyl < Methyl < Ethyl < Isopropyl D) Methyl < tert-Butyl < Isopropyl < Ethyl

14. Which of the following is a triplet carbene?

A) Dichlorocarbene B) Methylene (CH2) C) Dimethylcarbene D) Diphenylcarbene

15. The Curtius rearrangement involves the formation of which reactive intermediate?

A) Carbene B) Nitrene C) Carbocation D) Free radical

16. Which statement about carbocations is FALSE?

A) They are electron-deficient species. B) They are planar molecules. C) They are hybridized sp3. D) They are stabilized by electron-donating groups.

17. The negative charge in a carbanion is localized on:

A) The carbon atom B) An adjacent atom C) A heteroatom D) The counterion

18. Which of the following would most readily undergo homolytic cleavage?

A) CH3-Cl B) CH3-CH3 C) CH3-OH D) CH3-NH2

19. The geometry around the carbon atom in a carbene is typically:

A) Linear B) Trigonal planar C) Tetrahedral D) Pyramidal

20. The Hofmann rearrangement is initiated by the formation of:

A) A carbene B) A nitrene C) A carbocation D) A free radical

21. Which carbocation is least stable?

A) Benzyl carbocation B) Allyl carbocation C) Methyl carbocation D) tert-Butyl carbocation

22. Which of the following is a strong nucleophile and a strong base?

A) Carbocation B) Free radical C) Carbanion D) Carbene

23. The addition of halogens to alkenes often proceeds via a:

A) Carbanion intermediate B) Carbocation intermediate C) Free radical intermediate D) Nitrene intermediate

24. Dichlorocarbene (:CCl2) is an example of:

A) A singlet carbene B) A triplet carbene C) A nitrene D) A carbanion

25. The Wolff rearrangement converts an alpha-diazoketone into:

A) An ester or amide B) A ketone C) An aldehyde D) An alcohol

26. Which of the following is an electrophile?

A) Carbanion B) Carbene C) Carbocation D) Free radical

27. The stability of carbanions decreases with the introduction of:

A) Electron-donating groups B) Electron-withdrawing groups C) Alkyl groups D) Aromatic groups

28. Which reagent is commonly used to generate free radicals from peroxides?

A) Strong acid B) Strong base C) Heat or light D) Reducing agent

29. The carbon atom in a carbanion is typically hybridized:

A) sp3 B) sp2 C) sp D) d

30. The term 'radical scavenger' refers to a substance that:

A) Generates free radicals B) Reacts with and neutralizes free radicals C) Stabilizes carbocations D) Stabilizes carbanions

31. A carbene with two identical substituents on the carbon atom is called:

A) A singlet carbene B) A triplet carbene C) A symmetrical carbene D) An unsymmetrical carbene

32. The Schmidt reaction involves the reaction of a ketone or aldehyde with:

A) Hydrazoic acid B) Hydrozoic acid C) Hydrazine D) Hydroxylamine

33. Which reactive intermediate is involved in the Wurtz reaction?

A) Carbocation B) Carbanion C) Free radical D) Carbene

34. The stability order of free radicals is generally similar to that of:

A) Carbocations B) Carbanions C) Carbenes D) Nitrenes

35. Which of the following is a resonance-stabilized carbanion?

A) Methyl carbanion B) Ethyl carbanion C) Acetylide anion D) tert-Butyl carbanion

36. The insertion reactions of carbenes into C-H bonds are characteristic of:

A) Singlet carbenes B) Triplet carbenes C) Both singlet and triplet carbenes D) Nitrenes

37. In organic synthesis, which intermediate is often generated using organometallic reagents?

A) Carbocation B) Carbanion C) Free radical D) Carbene

38. The Fischer indole synthesis involves the cyclization of a phenylhydrazone, which can be thought of as involving:

A) A carbocation intermediate B) A nitrene intermediate C) A free radical intermediate D) A carbene intermediate

39. Which of the following is an example of a tertiary carbocation?

A) (CH3)2CH+ B) CH3CH2+ C) (CH3)3C+ D) CH3+

40. The stability of a carbanion is increased by:

A) Electron-donating groups B) Electron-withdrawing groups C) Steric hindrance D) Aromaticity

41. Which reaction involves the generation of a free radical from an azo compound?

A) Baeyer-Villiger oxidation B) AIBN decomposition C) Claisen rearrangement D) Diels-Alder reaction

42. The Hunt-Shorter rearrangement is a type of:

A) Carbocation rearrangement B) Carbanion rearrangement C) Free radical rearrangement D) Carbene rearrangement

43. Which intermediate is planar and has an empty p orbital?

A) Carbanion B) Carbocation C) Free radical D) Nitrene

44. The nucleophilic addition to carbonyl compounds often involves the formation of:

A) Carbocation B) Carbanion C) Free radical D) Carbene

45. Which statement about triplet carbenes is correct?

A) They have paired electrons with opposite spins. B) They have unpaired electrons with parallel spins. C) They are diamagnetic. D) They are more reactive than singlet carbenes in addition reactions.

46. The Tiffeneau-Demjanov rearrangement is a type of:

A) Carbocation rearrangement B) Carbanion rearrangement C) Free radical rearrangement D) Carbene rearrangement

47. Which of the following is a resonance-stabilized carbocation?

A) Methyl carbocation B) Ethyl carbocation C) Allyl carbocation D) Isopropyl carbocation

48. Which reactive intermediate is characterized by a carbon atom with a lone pair and two bonds?

A) Carbocation B) Carbene C) Carbanion D) Free radical

49. The Kolbe electrolysis of carboxylic acids produces:

A) Alcohols B) Aldehydes C) Alkanes D) Ketones

50. Which reactive intermediate has a pyramidal geometry at the central carbon atom?

A) Carbocation B) Carbene C) Carbanion D) Free radical

Reactive intermediates: carbocations, carbanions, free radicals, carbenes and nitrenes - Online Test

Test Results