Reaction Mechanism MCQs [Organic Chemistry]

1. Amongst the following which will show anti-Markownikoff addition in the absence of peroxides?

(A) None of A, B, and C

(B) CH₂=CH-CH₃

(C) CH₂=CH-Cl

(D) CH₂=CH-CF₃

2. According to transition state theory which is not the compulsory requirement for reaction to occur?

(A) Collision

(B) Energy of activation

(C) Transition state

(D) All of A, B, and C

3. With reference to collision theory, reaction takes place when molecules are ________.

(A) Colliding

(B) All of A, B, and C

(C) Activated

(D) In proper orientation

4. Which is an example of sigmatropic rearrangement?

(A) Benzidine rearrangement

(B) Diels-Alder reaction

(C) Hofmann bromamide reaction

(D) Claisen rearrangement

5. Formation of polyamide ‘Nylon’ from adipic acid and hexamethylene diamine is an example of

(A) Condensation reaction

(B) Condensation polymerization

(C) Copolymerisation

(D) Addition polymerisation

6. Homolytic fission of covalent bond results in the formation of ____ .

(A) Carbocations

(B) Both B and C

(C) Carbanions

(D) Free radicals

7. Kinetics of SN2 reactions are normally _____.

(A) Second order

(B) First order

(C) Pseudo-second

(D) None of A, B, and C

8. Which is true about carbanions?

(A) It has trigonal

(B) It has tetrahedral shape

(C) Carbanion carbon is sp³ hybridised

(D) Their order of stability is Pr. < Sec. < Ter.

9. The order of stability of free radicals

(A) I < II < III < IV

(B) IV < III < II < I

(C) II < I < III < IV

10. Which of the carbocation is likely stable?

(A) CH₂=CH-CH₂

(B) CH₃CH₂

(C) (CH₃)₂C⁺

(D) (CH₃)₂CH⁺

11. A reaction intermediate having only six electrons in the outer orbit of carbon but charge on it, is called ________.

(A) Carbocation

(B) Carbene

(C) Carbanion

(D) Free radical

12. Which is an electrophile?

(A) SO₃

(B) NF₃

(C) SO₂

(D) BF₃

13. Which is the reaction in which bond breaking and making processes take place simultaneously?

(A) Multistep reaction

(B) No mechanism reaction

(C) Free radical reaction

(D) Synchronous reaction

14. Free radicals are characterized by which of the following?

(A) Low reactivity

(B) Diamagnetism

(C) Loss of electrons

(D) Paramagnetism

15. Heterolysis of which bond is likely to form carbanion?

(A) C-Mg

(B) C-Cl

(C) C-O

(D) C-N

16. Entropy is a measure of

(A) Heat content

(B) Free energy

(C) Enthalpy

(D) Randomness

17. Dehydration of alcohol in acidic conditions is an example of _________ reaction

(A) E2

(B) SN1

(C) SN2

(D) E1

18. What is the type of reaction exhibited by alkanes?

(A) Depends on type of reagent

(B) Electrophilic substitution

(C) Nucleophilic substitution

(D) Free radical substitution

19. Which reactions are not shown by benzaldehyde?

(A) Perkin reaction

(B) Beckmann rearrangement

(C) Cannizzaro reaction

(D) Benzoin condensation

20. SN2 reactions are

(A) Usually occur through unimolecular

(B) Bimolecular

(C) Unimolecular

(D) None of A, B, and C

21. Cannizzaro reaction involves migration of which species?

(A) Proton

(B) Hydride ion

(C) Carbene

(D) Carbanion

22. The reactions of benzene ring are mainly

(A) Free radical substitution

(B) Nucleophilic substitution

(C) Nucleophilic addition

(D) Electrophilic substitution

23. Which is the reactions of carbonyl group?

(A) Nucleophilic substitutions

(B) Electrophilic additions

(C) Free radical addition

(D) Nucleophilic addition

24. The change in the state of hybridization of carbon in the reaction R-CN → RCONH₂ is

(A) sp³ to sp²

(B) sp² to sp

(C) sp to sp³

(D) sp to sp²

25. Diels-Alder reaction is an example of which type of reaction?

(A) Pericyclic reaction

(B) Nucleophilic addition

(C) Sigmatropic reaction

(D) Electrophilic addition

26. In the thermal conversion of cyclobutene to butadiene, the reaction is symmetry allowed if there is

(A) Reaction does not occur

(B) No correlation of symmetry

(C) Disrotatory opening of ring

(D) Conrotatory opening of the ring

27. Which bond is likely to break by homolysis?

(A) C-H

(B) C-Cl

(C) H-Cl

(D) H-O

28. Heterolysis of a ‘C-C’ covalent bond forms?

(A) Free radicals

(B) Both carbocations and carbanions

(C) Carbocations only

(D) Carbanions only

29. The SN2 mechanism occurs in _______.

(A) Three step

(B) One step

(C) Depends upon nucleophile

(D) None of A, B, and C

30. Which statements about the SN1 mechanism is false?

(A) The SN1 mechanism involves a single step

(B) SN1 reactions are unimolecular

(C) SN1 reactions are first order

(D) SN1 reactions usually occur in two steps

31. Which is the most reactive compound by the SN2 mechanism?

(A) CH3CH2CH2CH2Br

(B) (CH3)2CHCH2Br

(C) Both A & B are equally reactive

(D) None of A, B, and C can undergo SN2

32. Which is the most reactive compound by the SN1 mechanism?

(A) CH3CH2CH2Br

(B) Both A & B are equally reactive

(C) CH2=CHCH2Br

(D) None of A, B, and C can undergo SN1

33. Which statements is false?

(A) Both a & b

(B) SN2 reactions undergo partial inversion of configuration

(C) SN1 reactions undergo partial inversion of configuration

(D) None of the above

34. Which is most reactive as a nucleophile?

(A) CH3CH2O.

(B) CH3O.

(C) CH3NH2.

(D) PhO-

35. Which statements about the E1 mechanism is false?

(A) Reactions by the E1 mechanism are unimolecular in the rate-determining step

(B) Reactions by the E1 mechanism are multi-step reactions

(C) Reactions by the E1 mechanism usually occur in two step

(D) Reactions by the E1 mechanism are normally first order

36. In most of the cases,_________ compete with SN2 reactions.

(A) None of A, B, and C

(B) E1 Reactions

(C) Both A and B

(D) E2 Reactions

37. Which statements about the E2 mechanism is false?

(A) Reactions by the E2 mechanism usually occur in one step

(B) Reactions by the E2 mechanism are normally second order

(C) Reactions by the E2 mechanism usually occur in two steps

(D) Reactions by the E2 mechanism are always bimolecular

38. Which statements about mechanisms of elimination reaction is false?

(A) The E1 mechanism is usually unimolecular in the rate-determining step but leads to a second order rate law

(B) The E2 mechanism normally occurs under highly basic conditions

(C) The E2 mechanism is stereospecific

(D) The E1 mechanism does not require a base

39. Bromobenzene can’t undergo reaction due to which of the following?

(A) Br has poor electron withdrawing effect

(B) Phenyl groups is inductively electron donating

(C) The E2 mechanism is stereospecific

(D) Nucleophile is repelled by when it attacks on backside of SP2 carbon

40. In elimination reactions bulky leaving groups prefers to give

(A) Hoffmann product

(B) Saytzeff product

(C) Sometimes Saytzeff and sometimes Hoffmann product

(D) None of A, B, and C

41. In Saytzeff product a base nucleophile attacks the substrate

(A) Large sized

(B) Small sized

(C) Small or large sized (size of base no matters)

(D) None of A, B, and C

42. In elimination reactions, poor leaving group favors to follow which mechanism?

(A) E2 mechanism

(B) E1 mechanism

(C) Both a & b are equally preferable

(D) None of A, B, and C

43. Which type of solvent needed for the reactions to perform SN2 mechanism.

(A) Non-polar

(B) Polar aprotic

(C) Polar protic

(D) Aqueous

44. Mechanism of reaction may be studied with the help of

(A) Stereo chemical evidence

(B) Isotopic labeling

(C) Intermediate trapping

(D) All of A,B, and C

45. In the dehydrohalogenation of 2-chlorobutane, what is the main product?

(A) 2-Butene

(B) 1-Butanol

(C) 1-Butene

(D) 2-Butanol

46. Carbene intermediate is involved in which reaction

(A) Carbylamine reaction

(B) Reimer-Tiemann

(C) None

(D) Both