Questions about Substitution Reactions (Organic Chemistry)
20 multiple-choice questions about Substitution Reactions in Organic Chemistry, each with five alternatives (A–E). The correct answers with extended explanations are provided at the end.
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Multiple Choice Questions: Substitution Reactions (Organic Chemistry)
1. What is a substitution reaction?
A) A reaction where atoms are added to a molecule
B) A reaction where one atom or group replaces another
C) A reaction forming a polymer
D) A reaction involving only metals
E) A redox reaction involving oxygen
2. Which of the following is a typical nucleophile in substitution reactions?
A) H⁺
B) Cl⁻
C) CH₄
D) CO₂
E) Fe³⁺
3. In an SN1 reaction, what is the rate-determining step?
A) Attack of the nucleophile
B) Formation of the carbocation
C) Elimination of the base
D) Leaving group departure and nucleophile attack simultaneously
E) Rearrangement of alkyl group
4. Which of the following best describes an SN2 reaction mechanism?
A) Two-step with carbocation intermediate
B) Radical intermediate formation
C) One-step with backside attack
D) Elimination of HX
E) Formation of a double bond
5. What kind of solvent is preferred for SN1 reactions?
A) Nonpolar
B) Aprotic
C) Polar protic
D) Gaseous
E) Basic
6. Which of the following halides is most reactive in SN1 substitution?
A) Methyl chloride
B) Ethyl chloride
C) Propyl chloride
D) tert-Butyl chloride
E) Vinyl chloride
7. Which factor increases the rate of SN2 reactions?
A) Steric hindrance
B) Tertiary carbon
C) Polar protic solvent
D) Strong nucleophile
E) Stable carbocation
8. What type of product is formed in nucleophilic substitution reactions?
A) An alkene
B) An ether
C) A substituted compound
D) A polymer
E) A metal complex
9. In which reaction is inversion of configuration observed?
A) SN1
B) SN2
C) E1
D) Addition reaction
E) Aromatic substitution
10. Which of the following groups is a poor leaving group?
A) Cl⁻
B) Br⁻
C) I⁻
D) OH⁻
E) Tosylate
11. Which type of carbon center is most favorable for SN2 reactions?
A) Primary
B) Secondary
C) Tertiary
D) Allylic
E) Benzylic
12. What is the typical order of reactivity for SN2 (from fastest to slowest)?
A) Tertiary > Secondary > Primary
B) Primary > Secondary > Tertiary
C) Secondary > Primary > Tertiary
D) Primary > Tertiary > Secondary
E) Tertiary > Primary > Secondary
13. Why are tertiary halides unsuitable for SN2 reactions?
A) Lack of nucleophile
B) Too acidic
C) High steric hindrance
D) Not reactive
E) Unstable leaving group
14. What is the molecularity of an SN1 reaction?
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Tetramolecular
E) Depends on solvent
15. Which condition favors SN2 over SN1?
A) Polar protic solvent
B) Weak nucleophile
C) Tertiary alkyl halide
D) Polar aprotic solvent
E) High temperature
16. What is the common feature of good leaving groups?
A) High basicity
B) Large atomic radius and low electronegativity
C) Ability to stabilize negative charge
D) Strong nucleophilicity
E) Poor solubility
17. What happens to the reaction rate of SN1 if the concentration of the nucleophile is doubled?
A) It doubles
B) It triples
C) It stays the same
D) It is halved
E) It drops to zero
18. What type of substitution occurs in the reaction of benzene with Cl₂ in the presence of FeCl₃?
A) Nucleophilic aliphatic substitution
B) Electrophilic aromatic substitution
C) Free radical substitution
D) SN2
E) E1
19. Which class of substitution involves a nucleophile and is typical of alkyl halides?
A) Electrophilic substitution
B) Nucleophilic substitution
C) Aromatic substitution
D) Redox substitution
E) Acyl substitution
20. Which of the following is a common example of an SN2 reaction?
A) Reaction of tert-butyl bromide with water
B) Reaction of methyl bromide with hydroxide ion
C) Bromination of benzene
D) Formation of carbocation from propyl chloride
E) Dehydration of alcohol
- Questions about Esters (Organic Chemistry)
- Questions on Amines (Organic Chemistry)
- Questions on Alkyl Halides (Organic Chemistry).
✅ Answer Key with Extended Explanations
1. B – Substitution involves replacing one atom or group with another.
2. B – Cl⁻ is a common nucleophile in substitution.
3. B – SN1 rate-determining step is formation of the carbocation.
4. C – SN2 is a one-step process with backside attack.
5. C – SN1 prefers polar protic solvents to stabilize intermediates.
6. D – Tert-butyl chloride forms a stable carbocation, making it best for SN1.
7. D – Strong nucleophiles increase SN2 rates.
8. C – Product is a substituted organic molecule.
9. B – SN2 causes inversion due to backside attack.
10. D – OH⁻ is a poor leaving group unless protonated or modified.
11. A – SN2 works best with primary carbons due to low steric hindrance.
12. B – SN2: Primary > Secondary > Tertiary.
13. C – Steric hindrance prevents SN2 on tertiary carbons.
14. A – SN1 is unimolecular, depends only on alkyl halide concentration.
15. D – Polar aprotic solvents favor SN2 reactions.
16. C – Good leaving groups stabilize negative charge, like I⁻, Br⁻.
17. C – SN1 rate does not depend on nucleophile concentration.
18. B – Benzene + Cl₂ with FeCl₃ = electrophilic aromatic substitution.
19. B – Alkyl halides undergo nucleophilic substitution.
20. B – Methyl bromide + OH⁻ → classic SN2 reaction.
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