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65 views19 pagesHaloalkanes and Haloarenes
Haloalkane and haloarenes briefly explanation and simple easily examples with easy examples with images
Uploaded by
guitarsoul9876Copyright
© © All Rights Reserved
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/ 19
Ans.
HALOALKANES AND
HALOARENES ©
PREVIOUS YEARS’ QUESTIONS
(2017 )
Very Short Answer Type Questions [1 Mark]
ad the raanah of 1-Bromo-4-chlorobut-2-ene. {Delhi}
cl-én,—CH=CH—CH,—Br
Write the structure of 2, 4-dinitrochlorobenzene. [Delhi]
“I
NO,
NO,
Write the structure of 3-Bromo-2-methylprop-I-ene. [Delhi]
H,0=G—CH—Br
CH,
x
x
oat ae Cr which is an example of allylic halide? (Al
: [
is an example of allylic halide.
Out i and cr , which is an example of vinylic halide? [all
i io is an example of vinylic halide.
Sz aloarenes 285
Haloalkanes and H
\
7
4 i eal >
CH,CH,Cl
ale Cyn Ss CY “ad Avaten isan example of abenzyj,
5 ut of
halide? i
CHCL,
Ans. O is benzylic halide,
7. Write the IUPAC name of the following compound: .
¢u,
cH,—o0—C_cn,
cH,
5
Ans, 2-methoxy-2-methyl propane
. #8. Among the isomers of pentane (C;H,,), write the on
e which on photochemical
chlorination yields a single monochloride.
[Foreign)
CH, en
; hy
Ans. tact +Cl, Rue a) (ac +HCl
CH, CH,
Neopentane ‘Neopentyl chloride
(2,2-Dimethyl propane) (1-Chloro-2,2-dimethyl
propane)
Short Answer Type Questions [Il] [3 Marks]
9. Following compounds are given to you: [Delhi]
2-Bromopentane, 2-Bromo-2
methylbutane,
1-Bromopentane
‘h is most reac
tive towards S,.2 reaction.
() Write the compound wi
(i) Write the compound whi
(iii). Writ
Ans. (i) 1-Bromopentane is most
reactive towards S.
halide and has least ste
‘aric hinderance,
2-Bromopentane is optically active due to Presence of chiral carton
CHs—OH—CH,—CH,-CH,
Br
omo I butane because itis tertiary halide, undergoes nucleophilic
elimination reaction fastest.
2 reaction because it is primary
(i)
atom
(ii) 2-Bromo-2-meth
(286 Chapterwise CBSE PYQs (Chemistry) 19 ee
10. The following compounds are given to you:
2-bromopentane, 2-bromo-2-methylbutane, 1-Bromopentane
(a) Write the compound which is most reactive towards S,.2 reaction.
(6) Write the compound which is most optically activ.
(c) Write the compound which is most reactive towards f-elimination reaction.
Refer Ans, to Q.9.
———)
2016 }
Very Short Answer Type Questions [1 Mark]
I, Out of CH,—CH —CH,—Cl and Sed —Cl, which is more
CH, CH,
reactive towards S.1 reaction and why?
Ans. CHj—CH,—CH—Cl because secondary carbocation is more stable than
CH,
primary carbocation.
12. Write the structure of an isomer of compound C,H,Br which is most reactive
towards S,1 reaction. [Foreign]
~ CH,
Ans. CH,—C—CH, s the most reactive towards S,1 reaction.
Br
13. Which of the following reactions is S,1 type? [Foreign]
cH,
@ aati pee Yee’ Hittin
Bae CH; coy ee
CH, ‘ : CH,
Ans. (ii) is $1 type.
Haloalkanes and Haloarenes Short Answer Type Questions [II] [3 Marks]
14. Give reasons: Det
( C—Cl bond length in chlorobenzene is shorter than C—CI bond lengy,
in CH,—Cl.
(ii) The dipole moment of chlorobenzene is lower than that of cyclohexyi
chloride.
(iii) $1 reactions are accompanied by racemization in optically active ally,
halides.
Ans. (i) It is due to partial double bond character in three out of five Tesonating
structures, therefore, bond length is shorter than C—Cl (Single bond,
in CH,Cl and each carbon is sp® hybridised.
(i) Chlorobenzene is stabilized by resonance and there is +ve charge on ‘Cr
in 3 out of 5 resonating structures, therefore, it has lower dipole moment
than cyclohexyl chloride in which there is no such +ve charge.
(ii) Sy1 mechanism: When optically active alkyl halide undergoes S\1
Be Minis iilis accompanied by racemisation because intermediate
carbocation formed is sp* hybridised and planar. Nucleophile (OH?) has
equal probability of attacking it from either side leading to the formation
of equal amount of dextro and laevo-rotatory alcohols, i.e. racemic mixture
(optically inactive).
15. How do you convert: [All
() Chlorobenzene to biphenyl
(ii) Propene to 1-iodopropane
(iii) 2-bromobutane to but-2-ene.
Ans. (i) 2 4 = 2NaCl
s. (i) ()-a + Na + 2NaCl
Chlorobenzene Biphenyl
() CHy~CH=CH, + HBr P86, Cr cu cH,pr SL, cH,ci,CH!
Propene LBromopropane *°*°"® — Jodopropane
288 = Chapterwise CBSE PYQs (Chemistry)}—12 FT RRS! pe gy arrears Care i re
-_ meagre ionic Kt CEN: —> Coruclecphilicily 7) , so attodt jon
i Wt
it) ,
ae 6 HH—CH,—CH,, + KOH (alc) —> CH,—CH=CE 1—CH, + KBr + H,O
Buctene
Br
2.Bromobutane
te the major product(s) in the following:
iemetaeguyasen ees Aue Svvgibebe
@ iy Eh Bry, UV light
DB UV she 3,
N’
O;!
Ni - - - -
(9 20H, CH— CH, 3 a Ot sits Cae Bs
3
AEN Ss Covalént=3 nal CSU?
(ii) CHy—CH,—Br ———> ED
Br
|
CH,—CHy , CH—CH.
Ans. cr 8 Bry UV ight, Sols eae
O,N ON
@) BH —CH—CH, + 2Na— > CH —CH—CH—CH, + 2NaCl
cl CH, CH,
2,3-Dimethylbutane
1 AgCN,
(i) CH,—CH,—Br —“— CH,CH,NC + AgBr
17. Write the major products(s) in the following reactions: [Foreign]
CH,—OH
HO
wo HBr
cH,
ane
(i) CHIycxr,ct 2826" et
CH,—OH 3
oo
HO HO
Sf a HBr Cex
CH, “Br
iy GH,cr,c1 8°, c,cH,0-N=0
Haloalkanes and Haloarenes 289 Very Short Answer Type Questions [1 Mark] 2
18. Which would undergo S,2 reaction faster in the following pair:
C,H,—CH,—CH,—Br and Cpa CHE SH, TAL jig, A
Br
Ans. C,H,—CH,—CH,—Br will undergo S,2 reaction faster.
- CsH;—CH, 5 : '
19. Which would undergo S,2 reaction faster in the following pair:
CHj—CH —CH,—CH,—Br and CH,—CH,—CH —CH,—B,
cH, CH,
[AT Bhubanesy,
Ans. CH,—CH —CH,—C
»—Br will react faster.
CH,
20. Which would undergo Sy1 reaction faster in the following pair:
a
C,H;—CH,—Br and C,H,—CH —Br
cH.
3
FAT Guwahat
3
|
Ans. C5H;—CH —Br will react faster,
; cH,
CH,—CH,—Br and CH,—¢ —¢) H, ome
CH, 1
| ir
Ans. meee will react faster since '3° carbocation is more stable.
Br
22. Which would undergo $,2 reaction faster in the following pair and why?
Hy
CH,—CH,—Br and CH,—C__cH,
Br i
(Delhi; AI Trivandrum & Chennai
290 Chapterwise CBSE PYQs (Chemistry) —) oI ee le a
4 CH, —CH2— Br will react faster due to less stearie hindrance,
which would undergo Sy1 reaction faster in the following pair:
3. = J
(Hy -CH;—CH,—Br and CH,—CH—cH, [AI Allahabad & Dehradun}
Br
os cHs-GH—Cy will react faster.
Br
4, Which would undergo S,2 reaction faster in the following pair and why?
CH,—CH,—Br and CH,—CH,—I [Foreign]
9s: CH, —CH,—I will undergo Sx2 reaction faster because C—I bond has lower
pond dissociation enthalpy due to longer bond length than C—Br bond.
Short Answer Type Questions [Il] [3 Marks]
95, How do you convert the following:
@- Prop-1-ene to propan-2-ol
(i Bromobenzene to 2-bromoacetophenone
(iii) 2-bromobutane to But-2-ene [AI Ajmer]
HH
ans. (i) CHy-CH=CH,
r
(i) cH,coci "5
Br
(ii) cH, —114—CH,—CH + KOH(alc) coors
—> CH,—CH |—CH, + CH,—CH,—CH=CH, +KBr+H,O
(6) How do you convert the following:
(i) ethyl chloride is treated with Nal in the presence of acetone,
(i chlorobenzene is treated with Na metal in the presence of dry ether,
(ii) methyl chloride is treated with KNO,?
Write chemical equations in support of your answer. [AI Ajmer]
Ans. (i) Ethyl iodide is formed.
C,H,Cl + Nal
Acetone
CHI + NaCl
Haloalkanes and Haloarenes 291 Gi) Diphenyl is formed.
*¢ p-a VoNseey + 2NaCcl
ii) Methyl nitrite is formed
CH,Cl + K-+O—N=0 —~ CH,—O—N
27. Give reasons for the following:
(Benzyl chloride is highly reactive towards the $1 reaction.
Gi)_2-bromobutane is optically active but I-bromobutane is optically inactiy,
(iii) Electrophilic reactions in haloarenes occur slowly. __[AI Bhubaneswy
Ans. (i) Benzyl carbonation is stabilized by resonance.
(i) 2-Bromobutane is chiral as it contains asymmetric carbon atom, therefore
O + KCl
optically active, whereas I-chlorobutane is not chiral as it does not contai;
asymmetric carbon atom, therefore optically inactive.
(a) It is due to —I effect of halogens, it deactivates benzene Ting toward,
electrophilic substitution reactions.
28. Write IUPAC names of the following compound: fal,
@ asian a (ii) ir (iii) CH,=CH—CH,Cl
Br
‘Br
Ans. (i) 2-Bromobutane (@) 1, 3-Dibromobenzene (ii) 3-Chloroprop-1-ene.
29. Write the structures of the major product in each of the following reactions
@) Cy—cH—cH, eon,
(i) H,OJOH-
(i) pene aae aaes + KOH(aq) ——>
r Br
(iii) + Mg dryether [AT Guwahati)
- M unc (BAH,
Ans. (i) Sage CH, cet CH;CH,CH,OH
ie
(i) CHy—CH,—cH—cH, + KOH(aq) —> CH,—CH,—CH—CH, + KB"
Br ou
292 Chapterwise CBSE PYQs (Chemistry)—19 A eS ee
r Mgbr
Borate (7)
(i a O
sp, Write the structures of the major product in each of the following reactions:
ins H
) CH,-CH=CH, + Ho.
ethanol/heat
@ Fast CHa CCH, + KOH -
Br ¢
: anhyd AIC,
(i) + CH,cCOc1———4 {AI Trivandrum & Chennai]
OH
as, @) CHy—CH=CH, + H,O "5 cH,—CH—CH,
ethanol/heat
Eee IHC yy Snes CH, -CH=CH—CH,+ KBr + H,0
Br
r Br Br
8 ve may anya AlCl, COCH,
a) + CH,cocl———> +
COCH,
31. Write the structures of the major product in each of the following reactions:
@ cH,—CH=¢—CH + HBr —>
cH,
(i) CH,—CH,—CH,—CH—CHs + KOH
ethanol/heat
——
Br Br
Gy) 7 + cn,0 2S [AL Patna]
i
Ans. (i) CH, CH=F—CH, + HBr——> CH,—CHy—¢ —CH,
(oH CHs
293 |
Haloalkanes and Haloarenes i
¢thanoVheat,
@i) CH |s—CH, iC Hy [yp —-CH—CH, +KOH A——
|, CH,—CH,—CH=CH —CH, + KBr + 11,
r Br
anhyd. AICI,
(iii) + CH,CL = Q + HCl 5
cH,
32. How do you convert the following:
(i Prop-I-ene to 1-fluoropropane F
(ii) Chlorobenzene to 2-chlorotoluene
(iii) Ethanol to propanenitrile [AI Panchkula
Ans. (i) CH;—CH=CH, a ee CH, —CH,Br—" cH, CH,CH,F
i cin a
a
(ii) BS cHicl aS 4 HCI
(ii) CH,0H “, c,H,cl SS, c,H,c=N
33. Write the main products when
(n-butyl chloride is treated with alcoholic KOH.
(ii) 2, 4, 6-trinitrochlorobenzene is subjected to hydrolysis.
(iii) methyl chloride is treated with AgCN. [AI Panchkula]
Ans. (i) CH,CH,CH,CH,Cl + KOH(alc)>CH,—CH,—CH=CH, + KCI + H,0
OH
ON NO.
(i) ore ne a ar * + HCI
No,
iit) mi ae + a —— > CH,NSC + AgCl
34. (a) TheC—Clbond length in chlorobenzene is shorter than in CH, Cl, why’
(6) Arrange the following halides in order of increasing Sx2 reactivity:
CH,Cl, CH,Br, CH,CH,Cl, (CH,), CHCI
(294) Chapterwise CBSE PYQs (Chemistry)—12 —
(@) Write the TUPAC name of the following: [AI for Blind}
CH,
Cl
It is due to resonance, C—Cl bond is shorter due to sp? hybridization and
double bond character
() (CH,):CHCI < CH,CH,Cl < CH,CI < CH,Br
(@) I-chloro-6-methyl cyclohexene
s- |
5, Give reasons:
(a) Butyl bromide has higher boiling point than t-butyl bromide.
(b) Racemic mixture is optically inactive.
(c) The presence of nitro group (-NO,) at o/p positions increases the reactivity
of haloarenes towards nucleophilic substitution reactions. [Delhi]
. (a) It is because n-butyl bromide is a straight chain alkyl halide which has
more surface area than t-butyl bromide, therefore, more van der Waals’
forces of attraction, hence higher boiling point.
(b) Racemic mixture contains equal amount of dextro and laevo rotatory
compounds. Half of molecules rotate plane polarised light towards
left, remaining half towards right such that net optical rotation is zero.
Therefore, Racemic mixture is optically inactive.
(© -NO, stabilises the -ve charged ion formed during nucleophilic substitution
reactions of haloarenes, therefore, increases reactivity.
6, How can the following conversions be carried out:
() Aniline to bromobenzene
(ii) Chlorobenzene to 2-chloroacetophenone
(iii) Chloroethane to butane
Cr
Nu, NjCt
Br
ms ( i at a
) SS Benzene i ans
| “sot diazoninm romobenzene
chloride
[AI Allahabad & Dehradun]
Haloalkanes and Haloarenes 295 OF
1 y
Il AlCl, Wen,
(i) + CH,—C—Cl cc a
Acetyl chloride
Chlorobenzene (Ethanoyl chloride)
2-chloroacetophenone
es atrnoger0 7
HCAS ether Hy CH;~CH.—CH, +
thane Bune
(iti), CH\CH,
chloroethane
37. What happens when i
(i) Chlorobenzene is treated with Cl,/FeCl,,
(ii) ethyl chloride is treated with AgNO, _
(iii) 2-bromopentane is treated with alcoholic KOH?
Write the chemical equations in support of your answer,
IAT Allahabad & Dehrag
Ans. (i) o-dichlorobenzene and p-dichlorobenzene are formed.
cl eT (ai
Cl
+ cl, + +H
a
1, 2-dichlorobenzene
Shlorobe .
nies (0-dichlorobenzene)
1, 4-dichlorobenzene
(ii) Nitroethane will be formed. (p-dichlorobenzene)
CyH,Cl + AgNO, —— C,H,NOy + Agel
Ethyl chloride Nitroethane
(ii) 2-pentene will be formed as maj
jor product.
CH;—CH—CH,—CH,—CH,+KOH(ale.) —> CH —CH=
5 I
Br
2 pentene
2Bromopentane
38. (a) Why are alkyl halides insoluble in water?
() Why is Butan-1-o1 optically inactive but Butan-2-ol is optically active
(©) Although chlorine is an electron withdraw ing group,
Para- directing
yet it is ortho
in electrophilic aromatic substitution reaction, Why?
[Foreig
ible in water because they can neither form H-bon’
‘an break H-bonds between water molecules.
H—CH,—CH,+KBr+HJ
pent-2ene
Ans. (a) Alkyl halides are insolul
with water nor they ¢:
() Butan-1-o1 is achiral,
0 i.e. does not have chiral ‘C’ atom which is attacle
to four different gro
ups, therefore, it is optically inactive.
(296 Chapterwise CBSE PYQs (Chemistry) —19 em: - aaa |
Butan-2-ol is chiral, i.e. has chiral‘ atom, attached to four different groups.
| SH,
| HC eH CH,—CH,— CH,OH
! ie Butan-t achiral
CH,CH, } CH,CH, (tems tien
d(+) I)
Butan-2-ol
ect Ct Ch Fer
S-0=0-
Although-Cl is electron withdrawin,
due to +R effect, electron densit
g (-1 effect) but still o- and p-directing as
y is maximum at o- and p-positions
Very Short Answer Type Questions [1 Mark]
39. Identify the chiral molecule in the following pair:
va a
cd
ns. eat is chiral molecule.
cl
40. Draw the structure of 2- Bromopentane
1 3 2 5
ins. €,— Gx —CH, —CH, — CH,
lan
[Delhi(c)]
Br
|. Write structural formulae of the following compounds:
( 1-Bromo-4-chlorobenzene
(i) 1-chloro-4-ethyl cyclohexane.
[A]
Br cl
Ans. (i) (ii)
a C,H,
Haloalkanes and Haloarenes [297 i
Short Answer Type Questions [I] [2 Marks]
42. (i) Which alkyl halide from the following pair is chiral and undergoes fast,
S,2 reaction?
Opal,
(a) (6)
(ii) Out of Sy1 and S,2, which reaction occurs with’
(a) Inversion of configuration,
(b) Racemisation?
(Delhi
Ans. (i) ~~ Br will undergo $2 reaction faster.
is chiral
Br
(i) (a) Sy2 involves inversion of configuration.
(D) Sx1 involves racemisation,
43. Draw the structure of major monohalo product in each of the followin,
reactions:
® C)-on-
(i) (pon. —cr=cn, + HBr =,
Ans. (i) Cron 85.0) SO, + HCI
(i) Opca.-c= » + HBr Permits, (7) -CHy—CH,—CH,Br
44. Write chemical equations when:
[Delhi
(i) ethyl chloride is treated with aqueous KOH.
(ii) chlorobenzene is treated with CH,COCIL in presence of: anhydrous AICI,
{Foreign
Ans. () C,H.Cl + KOH (ag) —> G,H,OH + KCI
Ethyl chloride Ethyl miter
1 9 cl cl
cocn,
7) + CHC) 84, cr \ +HCl
Chlorobenzene Acetyl ehovide BE ccc
Bios COCH,
ea)
298 Chapterwise CBSE PYQs (Chemistry) —12 SS a
ys. @ Which alky! halide from the following pairs would you expect to react.
more rapidly by an S.2 mechanism and why? [Foreign]
rasmar zit CH, 5 CH,—CH,—CH,—CH,—Br
Br
(6) Racemisation occurs in S.1 reactions. Why?
CH,CH,CH,CH,Br will react faster towards $2 mechanism because it
has less stearic hindrance due to which nucleophile can readily attack
as compared to CH,—CH, »—-CH—CH,
ans. (2)
Br
()) InSy1 mechanism, intermediate carbocation is sp? hybridized and has planar
structure, therefore, there is equal probability of attacking nucleophile
from either of the side leading to the formation of equal amount of
dextro and laevo rotatory products leading to racemisation.
46. Write chemical equation when
(@) methyl chloride is treated with AgNO,.
(ii) bromobenzene is treated with CH,CI in the presence of anhydrous AICI,,
[Foreign]
fee) CHCl + AgNo, —> cH NSO + Agcl
Nitro methane
'
(i d: cH ane) +HCl
47. Write chemical equations when
( ethyl chloride is treated with alcoholic KOH.
(ii) chlorobenzene is treated with CH,Cl in the presence of-anhydrous AICI.
[Foreign]
Kou
Ans. (i) GH,CH,Cl “<“", CH,==CH, + KCl + H,O
1
(iy cS, cH > oy © +HCI
. Cr
1-Chloro-2-methylbenzene
Ren sree nce
Haloalkanes and Haloarenes 299 48. Write IUPAC names of the following compounds. Tare)
(a) CH,=CH — CH,Br
‘CCL
rs
&) cl—c—cal,
CCl,
Ans, (a) 3-Bromopropene
() Tris (trichloromethyl) chloromethane
49. Write structural formula of the following compounds [Ao
(i) 3-iodo-4-tert. butyl heptane
(ii) 4-bromo-3-methyl pent-2-ene
1 2 3 7.
Ans. (i) cH, —CH,—Gi— H—€n,—Cu,—CH,
1
CHy—¢—CH,
CH,
Br
(i) cH,—Cii—-c=cri-cH,
CH,
Short Answer Type Questions [I] [3 Marks]
50. (a) Draw the strructures of major monohalo products in each of the following
reactions:
@ ( )-cx,on oAaene
(i) (\-cx,c=cn, + HBr—,
(6) Which halogen compound in each of the following pairs will react faster
in S,2 reaction:
(i) CH,Br or CH,I (ii) (CH,),C—CI or CH,—Cl (aq)
Ans. (2) (i) ()-ex,0n aT ()-en,c
(300) Chapterwise CBSE PYQs (Chemistry)—19 Br
H,—CH—CH,
(i €\-cn,—-ci=cn, + HBr )—«
) @ GH will react faster
(ii) CHCl will react faster.
Very Short Answer Type Questions [1 Mark]
51. Write the IUPAC name of
H—CH,—CH=
CT ce [Delhi]
cl
‘ans. 4-Chloropent-l-ene
52, What happens when CH,—Br is treated with KCN? [Delhi]
‘Ans. CH,CN will be formed.
CH,Br + KCN ——> CH,C=
53. Write the IUPAC name of cH,cu—=Gi—¢—tu, [Delhi
‘Ans. 4-Bromo-4-methylpent-2-ene
54, What happens when ethyl chloride is treated with aqu
‘Ans. Refer Ans. to Q.44 (i).
55. Write the IUPAC name of (CH,),CHCH(C)CH,.
‘Ans. 2-Chloro-3-methylbutane
56, Which compound in the following pair undergoes
Den. AV
and {Delhi}
i 9
Ans. Be will undergo faster in Syl reaction.
g compound:
eous KOH? [Delhi]
[Delhi]
faster Syl reaction?
57. Write the IUPAC name of the followin: [Ay]
‘Hy
cH,—t—cH—CH,
CH,Cl
301
Haloalkanes and Haloarenes