Haloalkanes and Haloarenes: Class 12 Chemistry Notes & Important MCQs 

Introduction

Haloalkanes and Haloarenes are important classes of organic compounds studied in Class 12 Chemistry. These compounds contain halogen atoms and exhibit unique chemical properties. Understanding their classification, preparation, reactions, and applications is crucial for exams like West Bengal Higher Secondary (HS) Test.

Scroll down for MCQs  ↓  ↓  ↓ 

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Haloalkanes and Haloarenes: Overview

Haloalkanes (alkyl halides) and haloarenes (aryl halides) are organic compounds where halogens (F, Cl, Br, or I) replace hydrogen atoms in hydrocarbons.

Property	Haloalkanes	Haloarenes
Structure	Alkanes with halogen substitution	Aromatic rings with halogen substitution
Reactivity	More reactive due to C-X bond polarity	Less reactive due to resonance
Solubility	Insoluble in water, soluble in organic solvents	Similar solubility behavior
Boiling Point	Increases with molecular mass	Higher due to resonance stabilization

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Scroll down for MCQs  ↓  ↓  ↓ 

Classification of Haloalkanes and Haloarenes

1. Based on Number of Halogens

   • Mono-haloalkanes: Contain one halogen (e.g., CH3Cl - Methyl chloride)
   • Poly-haloalkanes: Contain multiple halogens (e.g., CCl4 - Carbon tetrachloride)

2. Based on Carbon Type (Haloalkanes)

• Primary (1°): Halogen attached to a primary carbon (e.g., CH3CH2Cl)
• Secondary (2°): Halogen attached to a secondary carbon (e.g., CH3CHClCH3)
• Tertiary (3°): Halogen attached to a tertiary carbon (e.g., (CH3)3CCl)

3. Based on Hybridization (Haloarenes)

• Aryl halides: Halogen directly attached to a benzene ring (e.g., Chlorobenzene)
• Benzyl halides: Halogen attached to a side-chain carbon of benzene (e.g., Benzyl chloride)

Most Important & Common MCQs for West Bengal HS Test

Basic Concepts

1. Which of the following is a primary alkyl halide?

   • a) CH3-CH2-CH2-Cl
   • b) CH3-CHCl-CH3
   • c) (CH3)3CCl
   • d) C6H5Cl
     Answer: a) CH3-CH2-CH2-Cl

2. The boiling point of haloalkanes increases with:

   • a) Increase in branching
   • b) Decrease in molecular weight
   • c) Increase in molecular weight
   • d) None of the above
     Answer: c) Increase in molecular weight

Reactions & Mechanisms

3. SN1 reaction follows:

   • a) Unimolecular mechanism
   • b) Bimolecular mechanism
   • c) Free radical mechanism
   • d) None of the above
     Answer: a) Unimolecular mechanism

4. Which reagent is used for dehydrohalogenation?

   • a) HCl
   • b) NaOH
   • c) Alcoholic KOH
   • d) Aqueous KOH
     Answer: c) Alcoholic KOH

5. Chlorination of methane gives:

   • a) CH3Cl
   • b) CH2Cl2
   • c) CHCl3
   • d) All of the above
     Answer: d) All of the above

Applications & Miscellaneous

6. Which of the following is used as an insecticide?

   • a) Chloroform
   • b) DDT
   • c) Iodoform
   • d) CFCs
     Answer: b) DDT

7. Which of the following reactions is used to prepare aryl halides?

• a) Wurtz reaction
• b) Sandmeyer’s reaction
• c) Finkelstein reaction
• d) Williamson synthesis
  Answer: b) Sandmeyer’s reaction

Nomenclature & Basic Concepts

8. Which of the following is a secondary haloalkane?

   • a) CH3CH2Cl
   • b) CH3CHClCH3
   • c) CH3CCl3
   • d) C6H5Cl
     Answer: b) CH3CHClCH3

9. The common name of CCl4 is:

   • a) Methyl chloride
   • b) Chloroform
   • c) Carbon tetrachloride
   • d) Methyl iodide
     Answer: c) Carbon tetrachloride

10. Which of the following has the highest boiling point?

• a) CH3Cl
• b) CH3Br
• c) CH3I
• d) CH3F
  Answer: c) CH3I

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Reaction Mechanisms & Properties

11. The SN1 reaction follows:

• a) First-order kinetics
• b) Second-order kinetics
• c) Zero-order kinetics
• d) None of these
  Answer: a) First-order kinetics

12. The SN2 mechanism is characterized by:

• a) Inversion of configuration
• b) Racemization
• c) Retention of configuration
• d) None of the above
  Answer: a) Inversion of configuration

13. Which reagent is used in Finkelstein reaction?

• a) NaCl
• b) NaI
• c) NaBr
• d) AgCl
  Answer: b) NaI

14. The Wurtz reaction is used to prepare:

• a) Alkanes
• b) Alkenes
• c) Alkynes
• d) Alcohols
  Answer: a) Alkanes

15. The order of reactivity of halides towards the SN1 reaction is:

• a) RF > RCl > RBr > RI
• b) RI > RBr > RCl > RF
• c) RCl > RBr > RI > RF
• d) RF > RI > RBr > RCl
  Answer: b) RI > RBr > RCl > RF

16. Which of the following undergoes the fastest SN2 reaction?

• a) CH3Cl
• b) CH3Br
• c) CH3I
• d) C6H5Cl
  Answer: c) CH3I

17. Dehydrohalogenation of alkyl halides in the presence of alcoholic KOH gives:

• a) Alkanes
• b) Alkenes
• c) Alkynes
• d) Alcohols
  Answer: b) Alkenes

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Electrophilic Substitution in Haloarenes

18. What is the major product when chlorobenzene undergoes nitration?

• a) o-Nitrochlorobenzene
• b) p-Nitrochlorobenzene
• c) Both (a) and (b)
• d) None of the above
  Answer: c) Both (a) and (b)

19. Which of the following reactions is used to prepare aryl halides?

• a) Wurtz reaction
• b) Sandmeyer’s reaction
• c) Finkelstein reaction
• d) Williamson synthesis
  Answer: b) Sandmeyer’s reaction

20. What is the hybridization of carbon in chlorobenzene?

• a) sp³
• b) sp²
• c) sp
• d) None of the above
  Answer: b) sp²

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Applications & Miscellaneous MCQs

21. Which of the following is used as a solvent for dry cleaning?

• a) Benzyl chloride
• b) Carbon tetrachloride
• c) Chlorobenzene
• d) Methyl chloride
  Answer: b) Carbon tetrachloride

22. Iodoform test is given by:

• a) Ethanol
• b) Acetone
• c) Both (a) and (b)
• d) None of the above
  Answer: c) Both (a) and (b)

23. Which of the following is a pesticide?

• a) Chloroform
• b) DDT
• c) Iodoform
• d) Freon
  Answer: b) DDT

24. Freons are used as:

• a) Refrigerants
• b) Anesthetics
• c) Cleaning agents
• d) Perfumes
  Answer: a) Refrigerants

25. Chloroform on exposure to air and light slowly gets oxidized to:

• a) CO2
• b) CCl4
• c) Phosgene
• d) HCl
  Answer: c) Phosgene

26. The depletion of the ozone layer is caused by:

• a) Chloroform
• b) Freons
• c) Iodoform
• d) Benzyl chloride
  Answer: b) Freons

27. Which of the following is a primary standard for the estimation of iodine?

• a) Chloroform
• b) Iodoform
• c) Benzyl chloride
• d) Bromoform
  Answer: b) Iodoform

28. Which of the following is used as an anesthetic?

• a) CH3Cl
• b) CHCl3
• c) CCl4
• d) C6H5Cl
  Answer: b) CHCl3

29. What is the main reason haloarenes are less reactive than haloalkanes?

• a) Resonance stabilization
• b) Inductive effect
• c) Hyperconjugation
• d) Tautomerism
  Answer: a) Resonance stabilization

30. Which of the following reactions involve free radical substitution?

• a) Wurtz reaction
• b) Halogenation of alkanes
• c) Sandmeyer’s reaction
• d) Finkelstein reaction
  Answer: b) Halogenation of alkanes

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Final Thoughts

These 30 most important MCQs on Haloalkanes and Haloarenes will help you ace the West Bengal Higher Secondary Exam. Practice them regularly, revise key concepts, and stay confident!

For more chemistry notes and MCQs, visit MightyKnowledge. 🚀

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Preparation of Haloalkanes and Haloarenes

Preparation of Haloalkanes

1. From Alcohols:
   $R-OH + HX → R-X + H2O$ (in presence of ZnCl₂, Lucas reagent)

2. From Alkanes (Free Radical Halogenation):
   $CH4 + Cl2 → CH3Cl + HCl$ (in presence of UV light)

3. From Alkenes (Addition Reaction):
   $CH2=CH2 + HBr → CH3-CH2Br$ (Markovnikov’s rule)

Preparation of Haloarenes

1. From Benzene (Electrophilic Substitution):
   $C6H6 + Cl2 → C6H5Cl + HCl$ (in presence of FeCl3)

2. From Diazonium Salts (Sandmeyer’s Reaction):
   $C6H5N2+Cl⁻ + CuCl → C6H5Cl + N2$
   

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Physical and Chemical Properties

Physical Properties

• Boiling points increase with molecular mass.
• Insoluble in water but dissolve in organic solvents.
• Density: Higher than corresponding alkanes.

Chemical Reactions

Haloalkanes:

1. Nucleophilic Substitution (SN1 & SN2 Reactions):
   $R-X + OH⁻ → R-OH + X⁻$ (Formation of Alcohols)

2. Elimination Reactions (Dehydrohalogenation):
   $CH3-CH2Cl + alc. KOH → CH2=CH2 + HCl$
   

3. Wurtz Reaction (Alkane Formation):
   $2R-X + 2Na → R-R + 2NaX$ (in presence of dry ether)

Haloarenes:

1. Electrophilic Substitution:

   • Nitration:
     $C6H5Cl + HNO3 → p-Nitrochlorobenzene + o-Nitrochlorobenzene$
   • Sulfonation:
     $C6H5Cl + H2SO4 → p-Chlorobenzenesulfonic acid$

2. Reduction (Clemmensen Reduction):
   

   $C6H5Cl + Zn + HCl → C6H6 + ZnCl2$

Uses of Haloalkanes and Haloarenes

• Chlorofluorocarbons (CFCs): Used in refrigerants (though banned due to ozone depletion).
• Chloroform (CHCl3): Used as an anesthetic.
• Iodoform (CHI3): Antiseptic.
• DDT (Dichlorodiphenyltrichloroethane): Insecticide.

Conclusion

Haloalkanes and Haloarenes are fundamental to organic chemistry. Understanding their properties, reactions, and uses is crucial for Class 12 Chemistry and competitive exams. Practice the MCQs above to strengthen your preparation for the West Bengal HS Exam.

~ For more study materials, visit MightyKnowledge. 🚀