Important Questions for Class 12 Chemistry Chapter 6 Haloalkanes and Haloarenes

Haloalkanes And Haloarenes

Question 1. Write The structure of the following compounds:

  1. 2-Cliloro-3-methylpentane
  2. 1-Chloro-4-methylcyclohexane
  3. 4-terl. ButyI-3-iodohcplane
  4. 1, 4-DibmmobiU-2- one
  5. 1-Bromo-4-sec, butyl-2-melhylbenzene

Answer:

Haloalkanes And Haloarenes Structure Of The Following Compounds

Question 2. Draw the structure of major monohalo products in each of the following reactions:

Haloalkanes And Haloarenes Structure Of Major Monohalo Products

Answer:

Haloalkanes And Haloarenes Structure Of Major Monohalo Products.

Question 3. Arrange each set of increasing boiling points.

  1. Bromomethane, Bromoform, Chloromethane, Dibromethane.
  2. 1-chloride, Isopropyl chloride, 1-chlorobutane.

Answer:

Haloalkanes And Haloarenes In Order Of Increasing Boiling Point

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Question 4. Which alkyl halide from the following pairs would you accept to react more rapidly by an SN2 mechanism? Explain your answer.

Haloalkanes And Haloarenes Alkyl Halide From SN2 Mechanism

Answer:

Haloalkanes And Haloarenes Alkyl Halide From SN2 Mechanism.

Question 5. In the following pairs of halogen compounds, which compound undergoes a faster SN1 reaction?

Haloalkanes And Haloarenes The Following Pair Of Halogen Compound Undergoes Faster Reaction

Answer:

Haloalkanes And Haloarenes The Following Pair Of Halogen Compound Undergoes Faster Reaction.

CBSE Class 12 Chemistry Chapter 6 Haloalkanes And Haloarenes Important Question And Answers

Question 6. Identify A, B, C, D, E, R, and R1 in the following:

Haloalkanes And Haloarenes Question 6

Answer:

Haloalkanes And Haloarenes Answer 6.

Question 7. Write the IUPAC name of the following:

Haloalkanes And Haloarenes IUPAC Name Of The Following

Answer:

  1. 4-Bromopent-2-ene
  2. 3-Bromo-2-methylbut-1-ene
  3. 4-Bromo-3-methyl pent-2-ene
  4. 1-Bromo-2-methylbut-2-ene
  5. 1-Bromobut-2-ene
  6. 3-Bromo-2-methylpropene

Question 8. Write the product of the following reactions:

Haloalkanes And Haloarenes Product Of The Following Reactions

Answer:

Haloalkanes And Haloarenes Product Of The Following Reactions.

Question 9. Haloalkanes react with KCN to form alkyl cyanides as the main product while AgCN forms isocyanides as the chief product. Explain.
Answer:

  • KCN is predominantly ionic and provides cyanide ions in solution. Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack place mainly through the carbon atom and not through the nitrogen atom since the C-C bond is more stable than the C-N bond.
  • However, AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanide as the main product.

Question 10. In the following pairs of hydrogen compounds, which would undergo SN2 reaction faster?

Haloalkanes And Haloarenes The Hydrogen Compound Undergoes SN2 Reaction Faster

Answer:

Haloalkanes And Haloarenes Primary Halide Undergoes SN2 Reaction Faster

  • It is a primary halide and therefore undergoes SN2 reaction faster.
  • As iodine is a better-leaving group because of its large size, it will be released at a faster rate in the presence of income nucleophiles.

Question 11. Predict the order of reactivity of the following compounds in SN1 and SN2 reactions:

  1. The four isomeric bromobutan.es
  2. C6H5CH2Br, C6H5CH(C6H5)BR, C6H5CH(CH3)Br, C6H5C(CH3)(C6H5)Br

⇒ \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Br}<\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}_2 \mathrm{Br}<\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3<\left(\mathrm{CH}_3\right)_3 \mathrm{CBr}\left(\mathrm{SN}_{\mathrm{N}} 1\right)\)

⇒ \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Br}>\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}_2 \mathrm{Br}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}\left(\mathrm{Br}_2 \mathrm{CH}_3>\left(\mathrm{CH}_3\right)_3 \mathrm{CBr}\left(\mathrm{S}_{\mathrm{N}} 2\right)\right.\)

Question 12. Although chlorine is an electron-withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions. Why?
Answer: Reactivity is thus controlled by the stronger inductive effect and orientation is controlled by resonance effect.

Question 13. Name the following halides according to the IUPAC system and classify them as alkyl, alkyl, benzene(primary, secondary, tertiary), vinyl, or aryl halide:

  1. \(\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}(\mathrm{Cl}) \mathrm{CH}_3\)
  2. \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{CH}\left(\mathrm{C}_2 \mathrm{H}_5\right) \mathrm{Cl}\)
  3. \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{C}\left(\mathrm{CH}_3\right)_2 \mathrm{CH}_2 \mathrm{I}\)
  4. \(\left(\mathrm{CH}_3\right)_3 \mathrm{CCH}_2 \mathrm{CH}(\mathrm{Br}) \mathrm{C}_6 \mathrm{H}_5\)
  5. \(\mathrm{CH}_3 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3\)
  6. \(\mathrm{CH}_3 \mathrm{C}\left(\mathrm{C}_2 \mathrm{H}_5\right)_2 \mathrm{CH}_2 \mathrm{Br}\)
  7. \(\mathrm{CH}_3 \mathrm{C}(\mathrm{Cl})\left(\mathrm{C}_2 \mathrm{H}_5\right) \mathrm{CH}_2 \mathrm{CH}_3\)
  8. \(\mathrm{CH}_3 \mathrm{CH}=\mathrm{C}(\mathrm{Cl}) \mathrm{CH}_2 \mathrm{CH}\left(\mathrm{CH}_3\right)_2\)
  9. \(\mathrm{CH}_3 \mathrm{CH}=\mathrm{CHC}(\mathrm{Br})\left(\mathrm{CH}_3\right)_2\)
  10. \(\mathrm{p}-\mathrm{ClC}_6 \mathrm{H}_4 \mathrm{CH}_2 \mathrm{CH}\left(\mathrm{CH}_3\right)_2\)
  11. \(\mathrm{m}-\mathrm{ClCH}_2 \mathrm{C}_6 \mathrm{H}_4 \mathrm{CH}_2 \mathrm{C}\left(\mathrm{CH}_3\right)_3\)
  12. \(\mathrm{O}-\mathrm{Br}-\mathrm{C}_6 \mathrm{H}_4 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{CH}_2 \mathrm{CH}_3\)

Answer:

Haloalkanes And Haloarenes Vinyl Or Aryl Halides

Haloalkanes And Haloarenes Vinyl Or Aryl Halides.

Question 14. Give the IUPAC names of the following compounds

  1. \(\mathrm{CH}_3 \mathrm{CH}(\mathrm{Cl}) \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3\)
  2. \(\mathrm{CHF}_2 \mathrm{CBrClF}\)
  3. \(\mathrm{ClCH}_2 \mathrm{C} \equiv \mathrm{CCH}_2 \mathrm{Br}\)
  4. \(\left(\mathrm{CCl}_3\right)_3 \mathrm{CCl}\)
  5. \(\mathrm{CH}_3 \mathrm{C}\left(\mathrm{p}-\mathrm{ClC}_6 \mathrm{H}_4\right)_2 \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3\)
  6. \(\left(\mathrm{CH}_3\right)_3 \mathrm{CCH}=\mathrm{CClC}_6 \mathrm{H}_4 \mathrm{I}-\mathrm{p}\)

Answer:

Haloalkanes And Haloarenes IUPAC Name Of The Following Compounds

Haloalkanes And Haloarenes IUPAC Name Of The Following Compounds.

Question 15. Write the structures of the following organic halogen compounds.

  1. 2-Chloro-3-methyl pentane
  2. p-Bromochlorobenzene
  3. l-Chloro-4-ethylcyelohexane
  4. 2-(2-Chlorophenyl)-1-iodooctane
  5. 2-Bromobutane
  6. 4-tert-butyl-3-iodoheptane
  7. 1-Bromo-4-sec-butyl-2-methyl benzene
  8. 1,4-Dibromobut-2-ene

Answer:

2-Chloro-3-methyl pentaneHaloalkanes And Haloarenes 3 Methyl Pentane

p-BromochlorobenzeneHaloalkanes And Haloarenes P Bromochlorobenzene

1-Chloro-4-ethylcyclohexaneHaloalkanes And Haloarenes 4 Ethylcyclohexane

2-(2-ChlorophenyI)-1-idodooctaneHaloalkanes And Haloarenes One Iodooctane

2-Bromobutane CHHaloalkanes And Haloarenes 2 Bromobutane

4-Tert-butyl-3-iodoheptaneHaloalkanes And Haloarenes 3 Iodoheptane

1-Bromo-4-sec-butyl-2-methyl benzeneHaloalkanes And Haloarenes Two Methyl Benzene

1,4-Dibromobut-2-eneHaloalkanes And Haloarenes Dibromobut Two Ene

Question 16. Which of the following has the highest dipole moment?

  1. CH2Cl2
  2. CHCl3
  3. CCl4

Answer:

Haloalkanes And Haloarenes The Highest Dipole Moment

CCl4 < CHCl3 < CH2Cl2

Question 17. A hydrocarbon C5H10 does not react with chlorine in the dark but gives a single monochrome compound C5H9Cl in bright sunlight. Identify the hydrocarbon.
Answer:

Haloalkanes And Haloarenes Cyclopentane

The reactions involved in the question are:

Haloalkanes And Haloarenes Mono Chlorocylopentane

Question 18. Write the isomers of the compound having the formula C4H9Br.
Answer: There are four isomers of the compound having the formula Chi I- Hr. These isomers are given below.

Haloalkanes And Haloarenes Isomers Of The Compound

7. Write the equations for the preparation of 1-iodobutane from

  1. 1-butanol
  2. 1-chlorobutane
  3. but-1-ene

Answer:

Haloalkanes And Haloarenes One Butanol

Haloalkanes And Haloarenes 1 Chlorobutane And But One Ene

Question 19. What are ambident nucleophiles? Explain with an example.
Answer: Ambident nucleophiles are nucleophiles having two nucleophilic sites. For example, nitrite ion is an ambident nucleophile.

Haloalkanes And Haloarenes Abident Nucleophile

Question 20. Which compound in each of the following pairs will react faster in SN2 reaction with Oil?

  1. CH3Br or CH3I
  2. (CH3)3CCl or CH3Cl

Answer: CH3-I is more reactive because I+ is a better-leaving group than Br+

Haloalkanes And Haloarenes SN2 Reaction With Oh

In the case of (CH3)3CCl. the attack of the nucleophile at the carbon atom is hindered by the presence of bulk)- substituents on that carbon atom bearing the leaving group.

Question 21. Predict all the alkanes that would be formed by dehydrohalogenation of the following halides with sodium ethoxide in ethanol and identify the major alkene.

  1. 1-Brorao-1-methylcyclohexane
  2. 2-Chloro-2-methyl butane
  3. 2,2, 3-Trirpethyl-3-bromopentane

Answer:

Haloalkanes And Haloarenes Dehydration Of The Following Halides With Sodium Ethoxide

Question 22. How will you bring about the following conversion?

  1. Ethanol to but-1-yne
  2. Ethane to broiuoethene
  3. Propene to I-nitropropane
  4. Toluene to benzyl alcohol
  5. Propene to propyne
  6. Ethanol to ethyl fluoride
  7. Bromomethane to propanone
  8. But-1-cue to but-2-ene
  9. 1-Chlorobutane to n-octane
  10. Benzene to biphenyl

Answer:

Haloalkanes And Haloarenes Answer 11

Haloalkanes And Haloarenes Answer 11.

Haloalkanes And Haloarenes Answer 11..

Question 23. Explain why

  1. The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?
  2. Alkyl halides, though polar, are immiscible with water?
  3. Grignard reagents should be prepared under anhydrous conditions.

Answer:

Haloalkanes And Haloarenes Chlorobenzene And Cyclohexylchloride

+M of -Cl and I of -Cl are in opposite directions so the dipole moment is decreased in chlorobenzene.

  1. No H-bonding of halide with water.
  2. Grignard reagents in the presence of moisture, react with H2O to give alkanes.

Haloalkanes And Haloarenes Grigrard Reagent

Question 24. Give the uses of freon 12. DDT, carbon tetrachloride, and iodoform.
Answer:

  • Uses of Freon-12 Freon-12 (dichlorodifluoromethane. CF2Cl2) is commonly known as CFC. It is used as a refrigerant in refrigerators and air conditioners.
  • The use of DDT (p-p-dichlorodiphenyltrichloroethane) is one of the best-known insecticides.

Uses of carbonletrachloride (CCI4)

  1. It is used for manufacturing refrigerants and propellants for aerosol cans.
  2. It is used as a solvent in the manufacture of pharmaceutical products.
  3. It is used as a fire extinguisher.

Uses of iodoform (CHI3) Iodoform was used earlier as an antiseptic. The antiseptic property of iodoform is due to the liberation of free iodine when it comes in contact with the skin.

Question 25. Write the structure of the major organic product in each of the following reactions.

  1. Haloalkanes And Haloarenes Structure Of Major Organic Product Reaction

Answer:

Haloalkanes And Haloarenes Major Organic Product Of The Reaction

Question 26. Write the mechanism of the following reaction:

Haloalkanes And Haloarenes Mechanism Of The Reaction

Answer: The given reaction is:

Haloalkanes And Haloarenes Mechanism Of The Reaction.

The given reaction is an SN2 reaction. In this reaction. CM acts as the nucleophile and attacks the carbon atom to which Br is attached. CN ion is an ambident nucleophile and can attack through both C and N. In this case, it attacks through the C-atom.

Haloalkanes And Haloarenes Ambident Nucleophile

Question 27. Arrange the compounds of each set in order of reactivity towards SN2 displacement:

  1. 2-Bromo-2-metln Ihutane. 1-Bromopentane, 2-Bromopentane
  2. 1-Bromo-3-methyl butane.2-Bromo-2-methyl butane.3-Bromo-2-inethyIhutane
  3. 1-Bromobutane. l-Bromo-2. 2-dimethyIpropane. 1-Bromo-2-methylbutane. 1-Bromo 3-methyIhutane

Answer:

Haloalkanes And Haloarenes In Order Of Reactivity Towards SN2 Displacement

(more branching at a nearer distance)

Hence, the increasing order of reactivity of the given compounds towards SN2 is:

1-Bromo-2,2-dimethy Ipropane < 1-Bromo-2-methy Ihutane < 1-Bromo-3-methylbutane < 1-Bromobutane.

Question 28. Out of C6H5CH2Cl and C6H5CHClC6H5, which is more easily hydrolyzed by aqueous KOH?
Answer: C6H5CHClC6H5 (more reactive)

Haloalkanes And Haloarenes More Easily Hydrolysed By Aqueous KOH

(more stable intermediate)

Question 29. p-Dichlorobenzene has higher m.p. and lower solubility than those of o-and m-isomers. Discuss.
Answer:

Haloalkanes And Haloarenes P Dichlorobenzene

p-Dichlorobenzene is more symmetrical than o-and m-isomers. For this reason, molecules of p-dichlorobenzene are more closely than o-and m-isomers in the crystal lattice. Therefore, more energy is required to break the crystal lattice of p-dichlorobenzene.

Question 30. How the following conversions can be carried out?

  1. Propene to propane-1-ol
  2. Ethanol to but-1-yne
  3. 1-Bromopropane to 2-bromopropane
  4. Toluene to benzyl alcohol
  5. Benzene to 4-bronitobenzene
  6. Benzyl alcohol to 2-phenylethanoid acid
  7. Ethanol to propane nitrile
  8. Aniline to chloro benzene
  9. 2-Chlorobutane to 3, 4-dimethyl hexane
  10. 2-Methyl-1-propane to 2-chloro-2-methyl propane
  11. Ethyl chloride to propanoic acid
  12. But-1-ene to n-butyliodide
  13. 2-chloropropane to 1-propanol
  14. Isopropyl alcohol to iodoform
  15. Chlorobenzene to p-nitrophenol
  16. 2-Bromopropane to 1-bromopropane
  17. Chloroethane to butane
  18. Benzene to diphene
  19. tert-Butyl bromide to isobutyl bromide
  20. Aniline to phenyl isocyanide

Answer:

Haloalkanes And Haloarenes Following Conversion Carried Out

Haloalkanes And Haloarenes Following Conversion Carried Out.

Question 31. The treatment of alkyl chlorides with aqueous KOH leads to the formation of alcohols but in the presence of alcoholic KOH, alkenes are major products, Explain.
Answer:

OH ion is highly solvated in an aqueous solution and as a result, the basic character of OH ion decreases. Therefore, it cannot abstract hydrogen from the β-carbon. So

⇒ \(\mathrm{R}-\mathrm{Cl}+\mathrm{Aq} \cdot \mathrm{KOH} \longrightarrow \mathrm{R}-\mathrm{OH}+\mathrm{KCl}\)

On the other hand, an alcoholic solution of KOFI contains an alkoxide (RO) ion. which is a strong base. Thus, it can abstract hydrogen from the β-carbon of the alkyl chloride and form an alkene by eliminating a molecule of HCl.

Haloalkanes And Haloarenes Alkyl Chloride And Alkene

Question 32. Primary alkyl halide C4H9Br(a) reacted with alcoholic KOH to given compound (b). Compound (b) is reacted with lIBr to give (c) which is an isomer of (a). When (a) is reacted with sodium metal it gives compound (d). C8H18 which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions.
Answer:

Two primary alkyl halides have the formula. C4H9Br. They are n-butyl bromide and isobutyl bromide.

Haloalkanes And Haloarenes Isobutyl Bromide

Therefore, compound (a) is either n-butyl bromide or isobutyl bromide.

Now, compound (a) reacts with Na metal to give compound (h) of molecular formula. C8H18. Which is different from the compound formed when n-butyl bromide reacts with Na metal. Hence. compound (a) must be isobutyl bromide.

Haloalkanes And Haloarenes N Butyl Bromide

Thus, compound (d) is 2. 5-Dimethylhexane.

It is given that compound (a) reacts with alcoholic KOH to give compound (b). compound (b) is 2-methyl propene.

Haloalkanes And Haloarenes 2 Methyl Propene

Also, compound (b) reacts with HBr to give compound (c) which is an isomer of (a). Hence compound (e) is -2-Bromo-2-methy propane.

Haloalkanes And Haloarenes 2 Bromo And Two Methylpropane

Question 33. What happens when

  1. n-butyl chloride is treated with alcoholic KOH?
  2. Broinohen/ene is treated with Mg in the presence of dry ether.
  3. Chlorobenzene is subjected to hydrolysis.
  4. Ethyl chloride is treated with aqueous KOH.
  5. Methyl bromide is treated with sodium in the presence of dry ether.
  6. Methyl chloride is treated with KCN.

Answer:

Haloalkanes And Haloarenes N Butyl Chloride

Chlorobenzene does not undergo hydrolysis under normal conditions. However, it undergoes hydrolysis when heated in an aqueous sodium hydroxide solution at a temperature of 623 K and a pressure of 300 atm to form phenol.

Haloalkanes And Haloarenes Chlorobenzene And Phenol

Haloalkanes And Haloarenes Ethyl Chloride And Methyl Bromide And Methyl Chloride

 

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