Here are 20 MCQs without the answers:
Which of the following alkyl halides undergoes SN1 reaction most readily?
- a) Methyl chloride
- b) Ethyl chloride
- c) Isopropyl chloride
- d) Tert-butyl chloride
What is the rate-determining step in the SN1 mechanism?
- a) Nucleophilic attack
- b) Formation of carbocation
- c) Departure of leaving group and nucleophilic attack together
- d) Rearrangement of the substrate
In SN2 reactions, which of the following is true about stereochemistry?
- a) Retention of configuration
- b) Racemization
- c) Inversion of configuration
- d) No effect on stereochemistry
Which type of solvent favors an SN2 reaction?
- a) Polar protic solvent
- b) Non-polar solvent
- c) Polar aprotic solvent
- d) Amphiprotic solvent
The order of reactivity of alkyl halides in SN2 reactions is:
- a) Tertiary > Secondary > Primary
- b) Primary > Secondary > Tertiary
- c) Secondary > Primary > Tertiary
- d) Tertiary > Primary > Secondary
Why do tertiary alkyl halides favor the SN1 mechanism?
- a) Low steric hindrance
- b) High carbocation stability
- c) Fast nucleophilic attack
- d) Poor leaving group stability
Which of the following nucleophiles will most likely favor an SN2 mechanism?
- a) H₂O
- b) CH₃O⁻
- c) NH₃
- d) ROH
In which of the following cases is racemization observed?
- a) SN1 reaction of chiral alkyl halide
- b) SN2 reaction of chiral alkyl halide
- c) Free radical substitution
- d) E2 reaction
Which of the following alkyl halides is most reactive in an SN2 mechanism?
- a) Methyl halides
- b) Primary alkyl halides
- c) Secondary alkyl halides
- d) Tertiary alkyl halides
The slowest step in an SN1 reaction is:
- a) Attack of nucleophile
- b) Formation of carbocation
- c) Rearrangement of the carbocation
- d) Departure of leaving group
Which of the following substrates is most reactive in an SN1 reaction?
- a) Vinyl chloride
- b) Chlorobenzene
- c) Methyl chloride
- d) Benzyl chloride
Which mechanism involves a concerted one-step process?
- a) SN2 mechanism
- b) SN1 mechanism
- c) Free radical mechanism
- d) E1 mechanism
Which of the following is a good leaving group for SN2 reactions?
- a) Cl⁻
- b) OH⁻
- c) H⁻
- d) NH₂⁻
Which of the following is the least likely intermediate in an SN1 reaction?
- a) Primary carbocation
- b) Tertiary carbocation
- c) Benzyl carbocation
- d) Secondary carbocation
What is the slowest step in an SN1 reaction mechanism?
- a) Attack of nucleophile
- b) Leaving group departure
- c) Slow formation of a carbocation
- d) Rearrangement of the substrate
Which of the following will undergo an SN2 reaction fastest?
- a) Secondary alkyl halide
- b) Tertiary alkyl halide
- c) Methyl halide
- d) Vinyl halide
What type of rate law does an SN2 reaction follow?
- a) Zero order
- b) Unimolecular
- c) Bimolecular
- d) First order
Which of the following favors SN2 reactions?
- a) Polar protic solvents
- b) Polar aprotic solvents
- c) Non-polar solvents
- d) Weak nucleophiles
Which of the following is the best leaving group for an SN1 reaction?
- a) Fluoride ion (F⁻)
- b) Bromide ion (Br⁻)
- c) Chloride ion (Cl⁻)
- d) Iodide ion (I⁻)
What is the first step in an SN1 reaction?
- a) Nucleophile attacks the carbon
- b) Formation of carbocation
- c) Formation of bond with nucleophile
- d) Leaving group departure
These MCQs will help in testing knowledge of SN1 and SN2 reactions
ANSWERS
Here are the answers with reasons:
d) Tert-butyl chloride
Reason: Tertiary alkyl halides form the most stable carbocations, favoring the SN1 mechanism.b) Formation of carbocation
Reason: The formation of a carbocation is the slowest step in the SN1 mechanism, making it the rate-determining step.c) Inversion of configuration
Reason: SN2 reactions involve backside attack, leading to inversion of configuration (Walden inversion).c) Polar aprotic solvent
Reason: Polar aprotic solvents do not solvate the nucleophile, making it more reactive for SN2 reactions.b) Primary > Secondary > Tertiary
Reason: SN2 reactions are hindered by steric factors, so less substituted alkyl halides react faster.b) High carbocation stability
Reason: Tertiary alkyl halides form stable carbocations, which is essential for the SN1 mechanism.b) CH₃O⁻
Reason: Methoxide ion (CH₃O⁻) is a strong nucleophile, favoring the SN2 mechanism.a) SN1 reaction of chiral alkyl halide
Reason: SN1 reactions involve a planar carbocation intermediate, leading to racemization.a) Methyl halides
Reason: Methyl halides have the least steric hindrance, making them highly reactive in SN2 reactions.b) Formation of carbocation
Reason: Carbocation formation is the slowest, rate-determining step in the SN1 mechanism.d) Benzyl chloride
Reason: Benzyl chloride forms a highly stabilized benzyl carbocation, making it very reactive in SN1.a) SN2 mechanism
Reason: SN2 is a concerted one-step process, involving simultaneous nucleophilic attack and leaving group departure.a) Cl⁻
Reason: Chloride ion is a good leaving group, making it suitable for SN2 reactions.a) Primary carbocation
Reason: Primary carbocations are highly unstable, making them unlikely intermediates in SN1 reactions.c) Slow formation of a carbocation
Reason: The slowest step in SN1 is the departure of the leaving group and the formation of the carbocation.c) Methyl halide
Reason: Methyl halides have no steric hindrance, making them most reactive in SN2 reactions.c) Bimolecular
Reason: SN2 reactions depend on the concentrations of both the nucleophile and the substrate, making it bimolecular.b) Polar aprotic solvents
Reason: Polar aprotic solvents enhance nucleophilicity without stabilizing the nucleophile, favoring SN2 reactions.d) Iodide ion (I⁻)
Reason: Iodide ion is the best leaving group because it is large and easily dissociates.b) Formation of carbocation
Reason: The first step in SN1 is the departure of the leaving group, leading to carbocation formation.
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