Haloalkanes and Haloarenes Previous Year Questions provides a comprehensive set of questions for Class 12 Chemistry students. This resource focuses on key concepts and reactions related to haloalkanes and haloarenes, essential for mastering the chapter. Students preparing for exams will find valuable practice questions that cover various aspects of the topic. The content is designed to help reinforce understanding and improve problem-solving skills in organic chemistry.

Key Points

  • Includes previous year questions on haloalkanes and haloarenes for Class 12 Chemistry.
  • Covers key concepts such as nucleophilic substitution reactions and bond lengths.
  • Provides explanations for the reactivity of different haloalkanes and haloarenes.
  • Features questions that help students prepare for board examinations effectively.
Nandini Raj
7 pages
Language:English
Type:Past Paper
Organic Chemistry
Nandini Raj
7 pages
Language:English
Type:Past Paper
Organic Chemistry
Nandini Raj
7 pages
Language:English
Type:Past Paper
Organic Chemistry
316

Haloalkanes and Haloarenes Previous Year Questions pdf

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PREVIOUS YEAR QUESTIONS
HALOALKANES AND HALOARENES
1. Chlorobenzene is extremely less reactive towards a nucleophilic substitution reaction. Give two reasons
for the same [March 2013] [2]
2. What happens when CH
3
−Br is treated with KCN? [March 2013] [2]
3. Give reason for the following:
(i) Ethyl iodide undergoes S
N
2 reaction faster than ethyl bromide
(ii) ()2-Butanol is optically inactive
(iii) C−X bond length in halobenzene is smaller than C−X bond length in CH
3
−X
[March 2013] [3]
3. Write the UPAC name of the following compound:
CH
3
−
C
⎯
CH
−
CH
3
CH
3
CH
3
Cl
[March 2013] [1]
4. (a) Why does p-dichlorobenzene have a higher m.p than its o- and m-isomers?
(b) Why is () Butan-2-ol is optically inactive? [March 2013] [2]
5. Write the UPAC name of the following compound
Cl
Cl
CH
3
[March 2013] [1]
6. Write the UPAC name of the following compound:
CH
3
−
CH
−
CH
2
−
CH
=
CH
2
Cl
[March 2013] [1]
7. (a) Draw the structures of major monohalo products in each of the following reactions
(i)
CH
2
OH
⎯⎯→
PCl
5
(ii)
CH
2
−
CH
=
CH
2
+ HBr
⎯→
(b) Which halogen compound in each of the following pairs will react faster in S
N
2 reaction:
(i) CH
3
Br or CH
3
(ii) (CH
3
)
3
C−Cl or CH
3
−Cl [March 2014] [3]
8. Write the mechanism of the following reaction
CH
3
CH
2
OH
⎯⎯ →⎯
HBr
CH
3
CH
2
Br + H
2
O [March 2014] [2]
9. dentify the chiral molecule in the following pairs
Cl
Cl
[March 2014] [1]
10. When the structure of the major product in each of the following reactions:
(i) CH
3
−CH=CH
2
+ H
2
O
(ii)
Br
CH
3
−
CH
2
−
CH
−
CH
3
+ KOH
⎯⎯⎯⎯→
ethanol / heat
(iii)
Br
+ CH
3
COCl
⎯⎯⎯⎯⎯→
anhyd.AlCl
3
[March 2015] [3]
11. Which would undergo S
N
2 reaction faster in the following pair:
CH
3
−
CH
2
−
Br and CH
3
−
C
−
CH
3
CH
3
Br
[March 2015] [1]
12. Out of CH
2
=CH−CH
2
Cl and CH
3
−CH
2
−CH
2
Cl, which is more reactive towards S
N
1 reaction?
[March 2016] [1]
13. What happens when:
(i) 2,4,6-trinitrochlorobenzene is treated with warm water
(ii) 2-chlorobutane is treated with alcoholic KOH
(iii) ethyl chloride is treated with Na metal in presence of dry ether
Write the equation involved in the above reactions [March 2016] [3]
14. Out of
X
and
X
, which is an example of vinylic halide? [March 2017] [1]
15. 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
N
2 reaction
(b) Write the compound which is optically active
(c) Write the compound which is most reactive towards -elimination reaction
[March 2017] [3]
16. Out of chlorobenzene and benzyl chloride, which one gets easily hydrolysed by aqueous NaOH and
why? [March 2018] [1]
17. (a) dentify the chiral molecule in the following pair:
OH
(i)
OH
(ii)
&
(b) Write the structure of the product when chlorobenzene is treated with methyl chloride in the
presence of sodium metal and dry ether.
(c) Write the structure of the alkene formed by dehydrohalogenation of 1-bromo-1-methylcyclohexane
with alcoholic KOH. [March 2018] [3]
18. Which alkyl halide from the following pair would you except to react more rapidly by S
N
2 mechanism?
CH
3
−
CH
2
−
CH
−
Br
CH
3
or
CH
3
−
C
−
Br
CH
3
CH
3
[March 2019] [1]
19. Give reasons for the following:
(a) The presence of −NO
2
group at ortho or para position increases the reactivity of haloarenes
towards nucleophilic substitution reactions
(b) p-dichlorobenzene has higher melting point than that of ortho or meta isomer
(c) Thionyl chloride method is preferred for preparing alkyl chloride from alcohols
OR
(a) Write equation for preparation of 1-iodobutane from 1-chlorobutane
(b) Out of 2-bromopentane, 2-bromo-2-methylbutane and 1-bromopentane, which compound is most
reactive towards elimination reaction and why?
(c) Give IUPAC name of
CH
3
−
CH
=
CH
−
C
−
CH
3
Br
CH
3
[March 2019] [3]
20. a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion: Boiling points of alkyl halides decrease in the order R – I > R – Br > R – Cl > R – F
Reason : van der Waal’s forces decreases with increase in size of halogen atom [March 2020] [1]
21. Justify and arrange the following compounds of each set in the increasing order of reactivity towards
the asked displacement
(a) 1 – Bromobutane 2 – Bromobutane 2 – Bromo – 2 – methylpropane (S
N
1 reaction)
(b) 1 – Bromobutane 2 – Bromobutane 2 – Bromo – 2 – methylpropane (S
N
2 reaction [March 2020] [2]
22. Enantiomers differs only in
(a) boiling point (b) rotation of plane-polarized light (c) melting point (d) solubility
23.
[Dec 2020] [1]
24. Which of the following is optically inactive?
(a) (+) - Butan – 2 – ol (b) (-) - Butan – 2 – ol
(c)
- Butan – 2 – ol (d) (+) – 2 – Bromobutane [Dec 2020] [1]
25. Which of the following has highest boiling point?
(a) C
2
H
5
– F (b) C
2
H
5
– Cl (c) C
2
H
5
– Br (d) C
2
H
5
– I [Dec 2020] [1]
26.
[Dec 2020] [1]
27. a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
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End of Document
316

Figures

[Sample paper 2021] [1]
𝐔𝐕 𝐥𝐢𝐠𝐡𝐭
1 = Bromomethane, 2= 2-Bromobutane, 3= 1-Bromobutane, 4= 2-Bromo-2-methylpropane

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FAQs

Why is chlorobenzene less reactive towards nucleophilic substitution?
Chlorobenzene is less reactive towards nucleophilic substitution reactions due to the resonance stabilization of the aromatic ring. The electron pairs on the halogen atom are in conjugation with the π-electrons of the ring, which decreases the availability of the carbon atom for nucleophilic attack. Additionally, the C−Cl bond in chlorobenzene is stronger compared to that in aliphatic haloalkanes, making it less susceptible to nucleophilic substitution.
What factors affect the reactivity of alkyl halides in SN2 reactions?
The reactivity of alkyl halides in SN2 reactions is influenced by steric hindrance and the nature of the halogen. For example, primary alkyl halides react faster than secondary and tertiary ones due to less steric hindrance. Among halogens, the order of reactivity is I > Br > Cl > F, as the bond strength decreases and the leaving group ability increases. This trend is crucial for predicting the outcomes of reactions involving alkyl halides.
What is the significance of the p-dichlorobenzene melting point compared to its isomers?
p-Dichlorobenzene has a higher melting point than its ortho and meta isomers due to its symmetrical structure, which allows for better packing in the solid state. This symmetry leads to stronger intermolecular forces, particularly van der Waals forces, making it more stable in the solid form. Understanding these differences in melting points is important for applications in organic chemistry and materials science.
How does the presence of a nitro group affect chlorobenzene's reactivity?
The presence of a nitro group at the ortho or para position in chlorobenzene significantly increases its reactivity towards nucleophilic substitution reactions. The nitro group is an electron-withdrawing group, which enhances the electrophilicity of the carbon atom bonded to the chlorine. This effect is due to the resonance structures that stabilize the transition state during the nucleophilic attack, making the reaction more favorable.
Which alkyl halide is most reactive towards SN1 reactions and why?
Among alkyl halides, tertiary alkyl halides are generally the most reactive towards SN1 reactions due to the stability of the carbocation formed during the reaction. The presence of alkyl groups stabilizes the positive charge on the carbocation through hyperconjugation and inductive effects. This stability makes the formation of the carbocation step more favorable, leading to a faster reaction rate.
What happens when ethyl chloride is treated with sodium metal in dry ether?
When ethyl chloride is treated with sodium metal in dry ether, a Wurtz reaction occurs, leading to the formation of butane. This reaction involves the coupling of two ethyl radicals generated from the alkyl halide, resulting in the formation of a higher alkane. The reaction conditions, including the use of dry ether, are crucial as they prevent the formation of side products.
Why does ethyl iodide undergo SN2 reactions faster than ethyl bromide?
Ethyl iodide undergoes SN2 reactions faster than ethyl bromide due to the weaker C−I bond compared to the C−Br bond. The bond strength affects the leaving group ability, with iodide being a better leaving group than bromide. This difference in leaving group ability is a key factor in determining the reaction rates of these alkyl halides in nucleophilic substitution reactions.

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