SN Reaction

1
1. Which of the following alkyl halide is most reactive towards substitution on reaction bySN1 mechanism
(1) (CH3)3 C —Br (2) (CH3)2—CH —Br (3) CH3—Br (4) CH3—CH2—Br

2. Which of the following undergoes nucleophilic substitution exclusively by SN1 mechanism

(1) Ethyl chloride (2) Isopropyl chloride (3) Benzyl chloride (4)Chloro benzene

3. Among the following, the one which reacts most readily with ethanol is
(1) p–nitro benzyl bromide (2) p–chloro benzyl bromide
(3) p-methoxy benzyl bromide (4) p–methyl benzyl bromide

4. SN1 reaction on optically active substrates mainly gives

(1) Retention in configuration (2) Inversion in configuration
(3) Racemic product (4) No product
5. The most reactive towards SN1 is
(1) PhCH2Cl (2) Ph Cl (3) PhCHCl(CH3) (4) p- NO2PhCH2Cl
6. In SN 1 the first step involves the formation of
(1) free radical (2) carbanion (3) cabocation (4) final product
7. The correct reactivity order of alcohols towards H–X will be
(I) CH2 CH—OH (II) CH2 CH—CH2O (III) CH3—CH2—OH (IV) CH3 CH CH3
OH
(1) II > I > III > IV (2) IV > III > II > I (3) II > IV > I > III (4) II > IV > III > I

8. Consider the following alcohols.

CH2OH CH2OH CH2OH CH2OH

O2N CH3O Br
I II III Iv

The order of decreasing reactivities of these alcohols towards nucleophilic substitution with HBr is
(A) III > I > IV > II (B) III > I > II > IV (C) I > III > IV > II (D) I > III > II > IV

9. In the reaction the major product formed is

(A) (B) (C) (D)

10. The order of decreasing SN1 reactivities of the halides is -

CH3CH2CH2Cl CH2 = CHCHClCH3 CH3CH2CHClCH3
I II III
(A) I > II > III (B) II > I > III (C) II > III > I (D) III > II > I
11. Unimolecular nucleophilic substitution [SN1] involves ....... steps, while bimolecular nucleophilic substitution
involves..... steps -
(A) Two, one (B) One, two (C) Two, two (D) One, three

12. Arrange the following compounds according to their relative reactivity with alcoholic AgNO3 -
t-Butyl chloride (I), sec-butyl chloride (II) and CCl 4 (III)
(A) I > II > III (B) III > II > I (C) II > I > III (D) II = III > I

13. Of the following, which is an SN1 reaction -

(A) (CH3)3CBr + H2O ––––– (B) CH3CH2CH2Cl + I– –––––
(C) (CH3)3CBr + CN– ––––– (D) CH3CHBrCH3 + OH(alc.) –––––
SN1, C H ONa
14.  
2 5
 Ether Ether is -
williamson

(A) (B) (C) Both correct (D) None is correct

15. Which one of the two iodine will be more reactive in the SN1 and SN2 reactions?
(a) A will be faster in SN1 reaction but slower in SN2
(b) A will be a faster both in SN1 and SN2 reactions
(c) A and B will be equally reactive
(d) B will be faster in both SN1 and SN2 reactions

16. In SN1 reaction, racemisation occurs if the reaction occurs at a stereogenic centre, however, 50 : 50 mixture of
enantiomers are rarely obtained, why?
(a) Usually one enantiomer is more stable than other
(b) Retention of configuration is always favoured in reaction
(c) Hydroxylic solvent favour retention of configuration
(d) There is steric hindrance to the approach of nucleophile from the front side as some of the leaving group
are not departed completely which favour inversion of configuration

17. Pick out the most reactive alkyl halide for an SN1 reaction -

(a) (b) (c) (d)

18. Pick out the compound which reacts fastest in the presence of AgNO3 :
(a) (CH3)3CCl (b) (CH3)2CHCH2Cl (c) (CH3)2CHCl (d) CH3CH2Cl

19. Which of the following compounds is most rapidly hydrolysed by SN1 mechanism-
(a) C6H5Cl (b) H2C = CH – CH2 – Cl (c) (C6H5)3CCl (d) C6H5CH2Cl

20. Which will give white ppt. with AgNO3?

(A) (B) (C) (D) Both A & C

21. Which of the following statement(s) is/are true for SN1 reaction -
(I) The rate of SN1 reaction depends on concentration of alkyl halide
(II) The rate of SN1 reaction depends on concentration of nucleophile
(III) SN1 reactions of alkyl halides are favoured by non-polar solvents
(a) Only I (b) Only II (c) Only III (d) Both I and III

22. From the following, pick out the potential energy profile for a SN1 reaction-

(a) (b)

(c) (d)

23. The most and least reactive electrophiles respectively in a SN1 reaction are-

(I) (II) (III) (IV)

(a) Both I and II (b) Both II and III (c) Both I and III (d) Both III and IV

24. Pick out the following factor(s) which promote a SN1 reaction :
(I) Temperature (II) Concentration of nucleophile
(III) Concentration of alkyl halide (IV) Aprotic solvents
(a) Both I and II (b) Both II and III (c) Both III and IV (d) Both I and III

25. Which of the following alkyl halides is respectively most and least electrophilic in SN1 reaction?

(a) Both I and III (b) Both II and III (c) Both III and I (d) Both I and II

26. Which of the following is true regarding a SN1 reaction-

(a) It would be faster at 25ºC than at 50ºC
(b) It would be faster in ethanol than in pentane
(c) Keeping the moles of reactants constant but doubling the quantity of solvent would decrease the rate by a
factor of 4
(d) Stereochemical inversion occurs exclusively
27. Rank the following molecules increasing in order of relative rate of SN1 solvolysis with methanol and heat-

(a) III < II < IV < V < I (b) II < III < IV < I < V
(c) V < IV < III < II < I (d) II < III < IV < V < I

28. Which is the most likely product when the following iodide is heated with water-

(a) (b) (c) (d)

29. What is the correct order of reactivity of the followings in hydrolysis reaction at elevated temperature-

(a) I < II < III < IV (b) IV < III < II < I (c) I < III < IV < II (d) I < IV < III < II

30. What is/are false regarding a SN1 reaction-

(a) Rate of reaction is faster in H2O than in C2H5OH
(b) The reaction usually have more than one transition states
(c) If a-carbon is chiral, partial racemisation and net inversion takes place
(d) Reaction occurs at faster rate if CH3O18H is used in place of CH3OH

31. Which of the following statements about a SN1 mechanism is true-

(a) The reaction is fastest with 3º halides
(b) The rate of reaction increases when the solvent is changed from acetone to ethanol
(c) The identity of the leaving group does not affect the reaction rate
(d) Both (a) and (b)

32. Which of the following will form a white precipitate on treatment with AgNO3(aq) :

(a) (b) (c) (d) Both (b) and (c)

33. Which of the following is most reactive in SN1 reaction -

(a) (b) (c) (d)

34. Which of the following is most reactive in SN1 reaction-

(a) (b) (c) (d)

35. A solution of (+)-1-chloro-1-phenylethane in toluene racemises slowly in the presence of a small amount of
SbCl5 due to the formation of-
(a) Carbanion (b) Carbine (c) Free radical (d) Carbocation

36. Arrange the following halides in decreasing order of reactivity in SN1 reaction :

(I) (II) (III) (IV)

(a) II > III > IV > I (b) IV > III > II > I (c) III > IV > II > I (d) I > II > III > IV

37. Arrange the following compounds in decreasing order of reactivity for hydrolysis reaction.

(I) PhCH2Br (II) (III) (IV)

(a) I > II > III > IV (b) IV > II > I > III (c) III > IV > II > I (d) IV > III > II > I

38. The increasing order of reactivity of the following bromides in SN1 reaction is-

(I) (II) (III) (IV)

(a) III > I > II > IV (b) III > I > IV > II (c) II > III > I > IV (d) II > I > III > IV

39. Which is the least reactive in solvolysis reaction-

(a) (b) (c) (d)

40. Arrange the following compounds in increasing order of their rate hydrolysis by SN1 mechanism :

(I) (II) (III) (IV)

(a) I < II < III < IV (b) III < I < II < IV (c) II < I < IV < III (d) III < II < I < IV
41. Arrange the following compounds in order of reactivity with alcoholic silver nitrate :-
C6H5CH2CH2Br(I), C6H5CHBrCH3 (II) and C6H5CH = CHBr (III)
(a) II > I > III (b) I > II > III (c) III > II > I (d) II = I > III

42. Which of the following statements are true for the S N 1 reactions of alkyl halides?
(a) The rate of an S N 1 reaction depends on the concentration of the alkyl halide and nucleophile both
(b) The S N 1 reactions of alkyl halides are favoured by polar solvents
(c) The rate of an S N 1 reaction depends on the concentration of the nucleophile
(d) The rate of an Sp reaction depends on the concentration of the substrate as well as that of the
nucleophile

43. Under conditions, the hydrolysis of neopentyl bromide, gives as the major product :

(a) ) (b) (c) (d) none of these

44. Consider the following groups:

(I) —OAc (II) —OMe (III) —O—SO2—Me (IV) —O—SO2—CF3
The order of leaving group nature is:
(A) I > II > III > IV (B) IV > III > I > II (C) III > II > I > IV (D) II > III > IV > I

45. Arrange the following compounds in order of decreasing rate of hydrolysis for SN1 reaction:

(I) CH2–Br (II) H3C CH2–Br

(III) CH3–CH2 CH2–Br (IV) CH CH2–Br

(A) II > III > IV > I (B) IV > III > II > I (C) III > IV > II > I (D) I > II > III > I

46. Consider the given reaction:

CH3–CH=CH–CH2–OH HBr
 [P] In the given reaction the product [P] is :
SN 1'

Br
|
(A) CH3–CH=CH–CH2–Br (B) CH 3  CH  CH  CH 2

Br
|
(C) CH2=CH–CH=CH2 (D) CH 3  CH  CH 2  CH 2  OH

47. The given compound CH3–O–CH2–Br gives which one of the following reactions:
(A) Only SN1 (B) Only SN2 (C) SN1 as well as SN2 (D) E1
48. Among the bromides I–III given below, the order of reactivity in SN1 reaction is:

(I) (II) (III)

(A) III > I > II (B) III > II > I (C) II > III > I (D) II > I > III

49. Consider the SN1 solvolysis of the following halides in aqueous formic acid:
Br
|
(I) CH  CH  CH 3 (II) (III) C6 H 5  CH  C 6 H 5 (IV)
|
Br
Which one of the following is correct sequence of the halides given above in the decreasing order of their
reactivity?
(A) III > IV > II > I (B) II > IV > I > III (C) I > II > III > IV (D) III > I > II > IV

50. In the given pair in which pair the first compound is more reactive than second for SN1 reaction.

Cl
(A) Cl CH2Cl (B)
Cl

Cl Cl

(C) (D)
Cl Cl
51. Which of the following is most reactive toward SN1.
CH2–Cl CH2–Cl CH2–Cl CH2–Cl

(A) (B) (C) (D)

H CH3 OCH3 NO2

52. Arrange the following compounds in decreasing order of their reactivity for hydrolysis reaction

(I) C6H5–CH2–Br (II) C6 H 5  CH  C 2 H 5 (III) (IV)

|
Br
(A) I > II > III > IV (B) IV > II > I > III (C) III > IV > II > I (D) IV > III > II > I
53. Which one of the following compounds will give enantiomeric pair on treatment with HOH?

C2H5 CH 3 H C2 H5
| | | |
(A) C6 H 5  C  I (B) CH 3  C  Br (C) C 6 H 5  C  Br (D) C 2 H 5  C  Br
| | | |
C2H5 C2 H5 D CH 3
 R1 R1
| |
HOH
54. For the given reaction R  C  X   R  C  OH Which substrate will give maximum racemisation?
| |
R2 R2

CH 3 CH 3
| |
(A) C6 H 5  C  Br (B) CH 2  CH  C  Br
| |
C2H 5 C2H 5

(C) (D)

55. In the given reaction: CH OH

 [X]
3 (excess)

(A) (B) (C) (D)

56. Which of the following can not give SN1 reaction easily?
Br
Br Br Br

(A) (B) (C) (D)

57. Correct order of rate of hydrolysis for following compounds is

[I] [II] [III] [IV]

(A) III > II > IV > I (B) I > II > III > IV (C) III > I > II > IV (D) III > II > I > IV
NaCN
58. In the given reaction: CH2–Cl   [X]
S 1
[X] will be:
N

(A) CH2CN (B) (C) NC CH3 (D) (A) and (C)

59. True statements regarding SN1 reaction is/are
(A) Perfect racemisation is observed (B) Only Walden inversion is observed
(C) Total retention of configuartion is observed (D) None of these

More Than One Correct

60. Which are possible products in following moist Ag O


2


(A) (B) (C) (D)

61. SN1 & SN2 is not favourable in

(A) H2C = CH–Cl (B) Ph–CH2–Cl (C) Ph–Cl (D) H2C=CH–CH2–Cl

62. SN1 & SN2 product are same in (excluding stereoisomer)

(A) (B) (C) (D) Ph  CH  CH  CH 3

| |
CH 3 Cl
63. When the reactants shown below undergo substitution, which of the products will form-

(a) (b) (c) (d)

64. If a pure dextrorotatory enantiomer of the substrate of the following reaction is boiled with water, the correct

statement(s) regarding SN1 product(s) is/are-

(a) Product would be pure laevorotatory

(b) Product would consists of both laevo and dextrorotatory enantiomers
(c) Product would be completely racemic mixture
(d) Product would be optically active with enantiomer of inverted configuration predominating

65. Which of the following can catalyse the following SN1 reaction-

(a) ZnCl2 (b) NaOH (c) NaCl (d) AgNO3

 ANSWER KEY
1. A 2. C 3. C 4. C 5. C 6. C 7. D 8. A
9. A 10. C 11. A 12. A 13. A 14. C 15. B 16. D
17. A 18. A 19. C 20. D 21. A 22. C 23. D 24. D
25. C 26. B 27. B 28. C 29. D 30. D 31. D 32. D
33. C 34. A 35. D 36. A 37. B 38. B 39. C 40. B
41. A 42. B 43. C 44. B 45. A 46. B 47. C 48. A
49. A 50. C 51. C 52. B 53. C 54. C 55. A 56. C
57. A 58. A 59. D
60. AB 61. AC 62. BC 63. ABCD 64. BD
65. AD