Free Nucleophilic Substitution MCQs with Answers
65 Nucleophilic Substitution MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Nucleophilic substitution replaces a leaving group in an alkyl halide when an electron-rich nucleophile attacks the carbon atom. The topic compares SN1 and SN2 mechanisms, including reaction conditions, substrate structure, solvent effects, nucleophile strength, carbocation formation and stereochemical changes, and distinguishes substitution from elimination.
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65 questions · page 2 of 4
- A. CH3-X
- B. (CH3)3 C-CH2 - X
- C. (CH3)2 CH - X
- D. (CH3)3 C - X
Explanation: A secondary alkyl halide has enough substitution to form a carbocation under SN1 conditions but is not so crowded that SN2 attack is…
Correct answer: (CH3)2 CH - X- A. C2H5O-
- B. SCN-
- C. NH3
- D. H3C+
Explanation: A nucleophile donates an electron pair, so C2H5O-, SCN- and NH3 can attack an electron-deficient centre.
Correct answer: H3C+- A. R-F
- B. R-C
- C. R-Br
- D. R-I
Explanation: For the same alkyl group, leaving-group ability increases from fluoride to iodide because the C-I bond is weaker and I- is more stable and…
Correct answer: R-I- A. E1 - reaction
- B. E2 - reaction
- C. SN1 - reaction
- D. SN2 - reaction
Explanation: SN1 reactions form a planar carbocation intermediate, allowing nucleophilic attack from either side and producing approximately equal…
Correct answer: SN1 - reaction- A. NH3
- B. Br+
- C. H+
- D. BF3
Explanation: An electrophile accepts an electron pair, as H+, Br+ and BF3 do because they are electron-deficient.
Correct answer: NH3- A. Zero
- B. First
- C. Second
- D. Third
Explanation: SN1 means unimolecular nucleophilic substitution because the slow step involves only the substrate forming a carbocation; therefore, rate…
Correct answer: First- A. HSO4-
- B. Cl-
- C. OH-
- D. Br-
Explanation: A good leaving group is a stable ion after it departs, and hydroxide is a strong base, so OH- is a poor leaving group.
Correct answer: OH-- A. 1
- B. 2
- C. 3
- D. 4
Explanation: In the Wurtz reaction, methyl iodide and ethyl iodide couple in three ways: methyl with methyl gives ethane, methyl with ethyl gives…
Correct answer: 3- A. BF3
- B. AlCl3
- C. SO3
- D. CN
Explanation: A nucleophile is a species that donates a pair of electrons to form a covalent bond.
Correct answer: CN- A. ŌH
- B. ŌR
- C. NH2
- D. I-1
Explanation: NH2 (amine) is correct because it is a weaker base compared to hydroxide ion and alkoxide ions, favoring substitution reactions over…
Correct answer: NH2- A. CH3 - NH2
- B. CH3 - CH2 -NH2
- C. OH|CH3 - CH - CH3
- D. O||CH3 - C - OH
Explanation: Ethylamine is the correct product of the reduction of acetamides. Acetamides, when reduced, undergo cleavage of the amide bond to form a…
Correct answer: CH3 - CH2 -NH2- A. (CH3)2CH − Cl CCl4/NaOH→ CH2)2 CH − OH
- B. C2H5Cl NaOH/H2O→ C2H5 − OH
- C. (CH3)3 CCl H2ONaOH→ (CH3)3C − OH
- D. (CH3)3C − Cl CCl4/NaOH → (CH3)3COH
Explanation: This reaction is more likely to proceed through SN1 mechanism because generally, tertiary alkyl halides are more reactive through this…
Correct answer: (CH3)3C − Cl CCl4/NaOH → (CH3)3COH- A. 1 - Bromobutane
- B. 2 - Bromobutane
- C. 1-Bromo-2-Methylpropane
- D. 2 - Bromo - 2 - Methylpropane
Explanation: C4H8O having one oxygen rules out the possibility of the intermediate compound being a primary alcohol as if it were to be a primary…
Correct answer: 2 - Bromobutane- A. Both are SN1
- B. (I) is SN1, (II) is SN2
- C. Both are SN2
- D. (I) is SN2, (II) is SN1
Explanation: In mechanism I, the reaction follows an SN2 pathway. This involves a single concerted step where the nucleophile attacks the substrate…
Correct answer: (I) is SN2, (II) is SN1- A. Free radical
- B. Carbanion
- C. Carbonium ion
- D. None of these
Explanation: In a carbanion carbon is bonded to three atoms or groups (trivalent) and has eight electrons(octet). It is an electron rich species.
Correct answer: Carbanion- A. Concentration of nucleophile doubled
- B. Concentration of substrate doubled
- C. Concentration of substrate tripled
- D. Concentration of substrate remains same
Explanation: The rate of SN2 reaction becomes doubled if the concentration of substrate is doubled.
Correct answer: Concentration of substrate doubled- A. BH3
- B. NH3
- C. -NH2
- D. -OH
Explanation: A nucleophile is a chemical species that donates a lone pair of electrons to form a chemical bond to another electron deficient species.
Correct answer: BH3- A. Primary and secondary
- B. Secondary and tertiary
- C. Primary and tertiary
- D. Primary, secondary and tertiary
Explanation: a) Primary and secondary:This option suggests that both primary and secondary halogenoalkanes can react with alkali by an SN2…
Correct answer: Primary and secondary- A. BF3
- B. SO3
- C. AlCl3
- D. CN
Explanation: Nucleophiles are elements/compounds containing extra pairs of electrons.
Correct answer: CN- A. A carbocation
- B. A free radical
- C. A carbanion
- D. An intermediate complex
Explanation: When nucleophilic substitution takes place bond between C and X dissociates.
Correct answer: A carbocation