Chapter Practice Problem CHEMISTRY

HALIDES (SN REACTIONS) IIT-JEE

1. Explain the following:
(i) t-Bu is Solvolysed in very acidic solutions.
(ii) t-BuCl is solvolysed more slowly than 2-chloro-2,3,3- 8. I II III
trimethyl butane.
(iii) t-BuCl is solvolysed much faster than 2-chloro-1,1,1- Decreasing order of SN1 reactivity of compounds
trifluoro-2-methyl propane. (A) I > II > III (B) I > III > II
(iv) t-BuCl is solovlysed more slowly in EtOH than in H2O. (C) II > III > I (D) III > I > II
2. Explain the reactions following SN1/SN2 mech: 9. Which will not give SN1 reaction with aq. AgNO3?
OTs
(i) CH3CH2CH2CH2 + Cl CH3OH
(A) (B) (C) (D)
O
O CH3 C OH
(ii) (CH3)3 C Br + CH3 C O 10. Which substrate on rkn with CH3OH gives dl mix.
(iii) H2O / EtOH
CH3 CH2CH CH3 + H2O (A) (B)
Cl
OMe

(iv) D.M.F. (C) (D)

SH

(v) t-BuOH
CH3I + (CH3)3C—O
11. 
Aq.
 ' X' product
AgNO3 (Major )
Cl CH3OH
(vi) + CH3OH
O (A) (B) (C) (D)
(vii) Cl + CH C O CH3COOH
3

3. Which of the following is correct (assume SN2): 12. Reactions not matched with correct major pdt. are?
Me D
(A) H NaCN
Cl H CN I: 
HBr

D Me
D D
(B) NaCN
H CH2Cl NC CH2 H
Me Me II: 
H2 O

Me
H C D LiAlD4
(C) optically inactive
Cl C H
18
Me III: 
H2 O

(D) All of these
4. In which step, inversion occurs:
Me Me
KCN / step (I) LAH / step (II)
H C Cl CN C H IV: 
CH3 OH

D D
(A) I (B) II (C) both (D) None
(A) I, II & III (B) I, II & IV (C) I, III & III (D) All
5. In which the order written is incorrect:
(A) Me  EtBr  Me2CHCl  Me3CCl (SN2 rkn) 18 

    13. O 
H3 O
 products X and Y are
(B) HO  MeO  Me2CHO  Me3 CO (leavability)
(C) Me3CCH2   Me2CHCl  Me2CHCH2Br  Me3CCH2F
(SN2 reactivity)
(D) None of these (A) , (B) ,
Me
H CH2 D NaCN
6. H Br Correct for the reaction is
D (C) , (D) ,
(A) product is optically inactive
(B) inversion at lower chiral carbon
(C) inversion at both the chiral carbon atoms 14. Correct reactivity order(s) for SN1 reaction is/are:
(D) None of these (1) Ph–Br < Ph–CH2–Br (2) Ph–Br > PhCH2Cl
7. The dielectric constants of the four solvents follows the
order S3 << S4 < S1 = S2. Among them only S2 and S3 can (3) O2N CH2–I > CH3 CH2–I
make hydrogen bonds. Which solvent will be most
(4) >
suitable for SN1 reaction?
(A) S1 (B) S2 (C) S3 (D) S4
(A) 1, 2, 3 (B) 2, 4 (C) 1, 4 (D) 2, 3, 4

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[2] Halides (SN Reactions) CPP-CHEMISTRY
st nd
15. Decreasing order of SN2 rkn with KI in acetone 23. 1 member is less reactive than 2 (SN1 rkn) in
Cl Br
(A) ,

(B) Br , Br

(C) O N CH2 Br , Me CH2 Br

2
(A) V > II > IV > I > III (B) II > V > I > IV > III
(C) IV > V > II > I > III (D) III > IV > II > V > I (D) Br , CH2 Br
16. the best alkylating agent in the reaction shown?
24. In which triplets at least two satisfy SN1:
(A) weak nucleophile, polar protic solvent, two step mech.
+ R–X
(B) carbonium ion intermediate, heterolysis due to
(A) (CH3)3CBr (B) CH2=CH–Br nucleophile, partial racemisation.
(C) C6H5CH2Br (D) (C) complete racemisation, polar protic solvent,
carbonium ion intermediate.
(D) All of these
17. Which reaction is most readily completed? OH

25. (i) One Eq. NaOH

  OH (A); Product (A) is:
(A) 
OH
 (B) 
OH
 (ii) MeBr
DMSO DMSO
OMe OH

(A) OH (B) OMe

 
(C) 
OH
 (D) 
OH
 OH
DMSO DMSO
(C) (D) None of these

18. (A): 3-chlorocyclopropene is solvolyzed in CH3OH at much

higher rate than 5-chlorocyclo penta-1,3-diene.
(R): The intermediate carbocation of latter is more stable 26. Br 1 Equivalent NaCN
than that for former. (A); Product (A) is:
(A) (A) & (R) are true & (R) explains (A).
(B) (A) & (R) are true & (R) does not explain (A). Br
(C) (A) is True, (R) is False
CN
(D) (A) is False, (R) is True Br Br CN
(A) (B) (C) (D)
19. (A): A bridge head halide like norboryl bromide is inert for
CN CN Br Br
SN1 reaction Br
Br OH
(R): Carbonium ion at bridgehead position cannot be
formed because planarity is not possible. OH
27.
(A) (A) & (R) are true & (R) explains (A).
(B) (A) & (R) are true & (R) does not explain (A). H H
(C) (A) is True, (R) is False (I) (II)
(D) (A) is False, (R) is True Mechanism of Conversion of I to II:
(A) takes place by SN1 (B) takes place by SN2
20. 
H2 O/ Acetone
 Possible total product and (C) takes place by SNi (D) does not take place

fractional distillation parts are respectively. 28. Rate of SN2 will be negligible in:
Br Br Br Br
(A) 2, 1 (B) 4, 2 (C) 6, 3 (D) 8, 4
21. Mark true false statements for reaction (A) (B) (C) (D)
CH3
KI131
H I   Product
C6H13 DMSO 29. The greater SN2 reaction is in each pair is for?
2-Iodooctane O
S1: Rate depends on both [R–I] and [Nucleophile] (P) (I) Br CN (II)
+ O CH3 + CN
S2: Loss of optical activity is twice of gain of radioactivity.
(Q) (III) H3C Br + SH (IV) H3C Br + CH3SH
S3: Each molecule suffers Inversion of configuration
S4: At equilibrium mixture is optically inactive (R) (V) Br + Cl (VI) Br + I in DMSO
(A) T T T T (B) T T F F (C) T F T F (D) T T T F
22. Maximum racemisation will take place in solvolysis of (S) (VII) Br + Cl (VIII) Br + I in CH3OH
which optically active t-alkyl chloride? P Q R S P Q R S
CH2D Me Me CHMe 2
(A) I IV VI VIII (B) II III V VIII
(i) Me Cl (ii) Et Cl (iii) Ph Cl (iv) Ph Cl
(C) I III V VIII (D) I III V VII
CHD 2 CH2D CH2D CH2D
(A) (i) (B) (ii) (C) (iii) (D) (iv) 30. Decreasing nucleophilicity in polar protic solvent is
(I) CH3CH2CH2O (II) CH3CH2CH2S (III) CH3CH2COO

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

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CPP-CHEMISTRY Halides (SN Reactions) [3]

O NaNH 2 H2O/Acetone
31. S (CH2)4 CH2 Cl (A); Product (A) is: P1
di methoxy ethane 40. Br CH2OH HBr
O (Major)
P2
O O
(A) S (CH2)3 CH CH2 (B) S P1 and P2 are respectively:
O O (A) HO CH2OH , Br CH2OH
O
(C) S (CH2)4 CH2 NH2 (D) None (B) HO CH2OH , Br
O Br
32. Which will form a pair of enantiomers? Br
CN CH2OH ,
(A) (B) I H H2O (C)
I H DMSO HOH 2C
Br
I OH Br
H3C OH
(C) (D) CH3OH
(D) ,
DMF I H
OH Br
33. Which of the following statements is true?
– 41. In the following reaction product is:
(A) CH3CH2S is both a stronger base and more
–
nucleophilic than CH3CH2O
–
(B) CH3CH2S is a stronger base but is less nucleophilic
– NaBr KOH/DMSO
than CH3CH2O
– (2) (3)
(C) CH3CH2S is a weaker base but is more nucleophilic
–
than CH3CH2O
–
(D) CH3CH2S is both a weaker base and less
–
nucleophilic than CH3CH2O
O O - (A) (B)
O O
- -
34. CF 3 S O C6H5 S O -
CH3 C O
O O
(I) (II) (III) (IV) (C) A & B both (D)
Decreasing leaving tendency in SN reaction is
(A) I > II > III > IV (B) I > II > IV > III
(C) IV > I > II > III (D) IV > III > II > I
O 42. X+Y
35. (P) (Q) (R) (S)
(Y is hydrocarbon)
Br Br Br Br
which of the following statement is correct.
Time for formation of ethers while ethanolysis in same (A) Step-1-is an SN2 reaction
condition are tP, tQ, tR, tS. Which is correct? (B) Y is CH3(CH2)2CH3
(A) tQ < tP < tS < tR (B) tP < tQ < tR < tS (C) X = cyclopentadiene
(C) tQ < tS < tP < tR (D) tP < tR < tQ < tS nd
(D) the nucleophile in 2 reaction is
Me Me Me
36. Na, heat Cl EtOH OEt
H OH H 1 O Na + H 2 Cl 43. Rate R1
D R1 D D R2
Which of the following is/are correct? CH3 EtOH CH3
(A) In R1 inversion occurs Cl OEt Rate R2
(B) In R1 inversion does not occur
(C) In R2 inversion around (1), but not around (2) Cl EtOH OEt
(D) In R2 inversion around (2), but not around (1) Rate R3

37. The slowest rate of reaction (SN2) is in? Which of the following is correct?
(A) (CH3)3C CH2Br + (A) R1 > R2 > R3 (B) R3 > R2 > R1
O
(C) R2 > R1 > R3 (D) R2 > R3 > R1
(B) CH3 Br + CH3 O 44. Bottles containing PhI & PhCH2I lost their original labels.
Labelled as (A) and (B), they were separately boiled with
(C) (CH3)3C CH2Cl + CH3 O NaOH solutions. The end solution in each case was
(D) (CH3)3C CH2Cl + made acidic with dilute HNO3 and addition of AgNO3
O
solution to (B) gave yellow precipitate. Which is true?
(A) Addition of HNO3 was unnecessary
Me LAH
(A) (B) (A) was PhI
38. H Cl , optical nature (A) & (B) are (C) (A) was PhCH2I (D) (B) was PhI
H D LAD
(B)
Me 45. Esterification of (–)-lactiac acid with methanol yields (+)-
(A) active, active (B) inactive, inactive methyl lactate. Assuming that there are no side
(C) active, inactive (D) inactive, active reactions, what is true about this reaction?
OH CH3OH OH
R R R OH OCH3
39. – – HCl
Nu H X Nu C X Nu +X
H O O
D D H D (-) (+)
The T.S. is attained at t = t0 and the product is obtained at (A) SN2 & inversion of configuration on chiral center
t = t1. The % s-character of attacked carbon at t = t2 (0 < t2 (B) SN1 with inversion of optical rotation
< t0) and at t = t0 are: (C) A diastereomer has been produced
(A) 25, 33.3 (B) 20, 33.3 (C) 28, 66.7 (D) 29.5, 33.3 (D) Optical rotation is not directly related to configuration &
change in rotation is a coincidence
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[4] Halides (SN Reactions) CPP-CHEMISTRY

46. The order of reactivity for SN1 reaction is: 55. In which of the following pairs first member is less
O
reactive than second member towards SN1 reaction:
(I) (II) (III) Cl Br

Br Br
(A) ,
Br
(A) III > I > II (B) III > II > I (C) II > III > I (D) II > I > III
Br
(B) Br , Br
47. aq KOH
'P' (C)
O2N CH2 Br , Me CH2 Br
OH OH
(A) P is ; SN2 (B) P is ;SN1
(D) Br , CH2 Br
(C) P is ; E2 (D) no reaction is possible
NaH
Me Me 56. (R)-2-butanol A
48.
H Cl LiAlH4 H Cl LiAlD4
(A), (B), (assume SN2) SN 2 (S)-2-chlorobutane
H D H D TsCl
Me Me
P1
Optical nature of (A) and (B) are:
A
(A) active, active (B) inactive, inactive B P2
SN 2
(C) active, inactive (D) inactive, active
Me (A) P1 is optically active (B) P1 & P2 are enantiomers
H CH2D NaCN (C) P1 & P2 are diastereomers (D) P2 is optically active
49. Product ; Which is correct?
H Br 57. Which of the following is/are correct?
D Me Me Me
Na, heat +
(A) product is optically inactive R1 : H OH R2 : H O Na + H Cl
1 2
(B) configuration about lower chiral carbon is inverted D D D
(C) configuration about both chiral C atoms is inverted (A) In R1 inversion occurs
(D) None of these (B) In R1 inversion does not occur
CH3 (C) In R2 inversion around (1) occurs but not around (2)
H Br (D) In R2 inversion around (2) occurs but not around (1)
H H + NaN 3 (1 eqv) Product
50. ; Product is 58. The correct statement(s) for a SN reaction is
H Cl
(A) During SN1 and SN2 mechanism both electron
CH3
deficient carbon must attain planar geometry.
CH3 CH3
CH3 CH3 (B) SN1 is favoured by tert. carbocation & strong nucleophile.
H N3 N3 H N3 H H N3 (C) SN2 reactions will show inversion of configuration.
(A) H H (B) H H (C) H H (D) H H (D) Aprotic polar solvent promotes SN1 reaction.
H Cl Cl H H Cl Cl H
59. Which is correctly method?
CH3 CH3 CH3 CH3
Reactant Product Mech.
51. Which will react faster with KI/acetone in given pair? –
CH2Br CH2CH2Br (A) +PhSH/OH PhSMe SN1
O

(i) & (ii) CH3 O S C6H5 & CH3Cl

O B (B) + CH3OH SN2
A B A
(A) A, A (B) B, B (C) B, A (D) A, B + HCl
(C) SN2
52. Arrange in increasing order of reactivity toward AgNO3.
Cl Cl
Cl

;
; (D) + aq AgNO3 SN1

60. Write conformational structures for SN products of

(I) (II) (III)
following deuterium-labeled compounds:
(A) III < II < I (B) I < II < III (C) I < III < II (D) III < I < II Cl
Cl
 
 
53.
H Br
KOH
(a) H 
CH3 OH
 (b) H 
CH3 OH

C ? D
D
H3C CH2CH3 SN2 H H
Cl Cl
(A) (R)-2-Butanol (B) (S)-2-Butanal  

(C) (S)-2-Butanol (D) None (c) H H 

CH3 OH
 (d) CH3 
H2 O
CH3 OH

H
D
54. Which of the following statement is incorrect for SN2? D
(A) The reaction follows second order kinetics
(B) The rate depends upon the [nucleophile]
(C) one step reaction through formation of transition state
(D) The rate is increased on changing the solvent from
polar aprotic to polar protic
ANSWER KEY
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
– – D A – B B B D C C D B C A C C C A B
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
A D C D A C D C C D D B C B A BD D A D C
41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
B B D C D A D A B C A B A D C AC BD AC D –
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