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Haloalkanes and Haloarenes: questions with answers

Class 12 Chemistry, Chapter 6 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.

How to teach this chapter · Common misconceptions & worked visual for this chapter

Classification, nomenclature, and the carbon–halogen bond

Question 1

Which statement gives the sound Class XII chemistry for ‘Classification, nomenclature, and the carbon–halogen bond’?

  1. (a)The same conclusion about classification, nomenclature, and the carbon–halogen bond remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.
  3. (c)Only the name of the substance is needed for classification, nomenclature, and the carbon–halogen bond; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)For classification, nomenclature, and the carbon–halogen bond, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(b) Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.

Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.

Question 2

Which principle should be retained when checking an inference about ‘Classification, nomenclature, and the carbon–halogen bond’?

  1. (a)Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.
  2. (b)For classification, nomenclature, and the carbon–halogen bond, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  3. (c)Only the name of the substance is needed for classification, nomenclature, and the carbon–halogen bond; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)The same conclusion about classification, nomenclature, and the carbon–halogen bond remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
Show answer

(a) Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.

Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.

Question 3

Which statement correctly governs a new case involving classification, nomenclature, and the carbon–halogen bond?

  1. (a)Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.
  2. (b)The same conclusion about classification, nomenclature, and the carbon–halogen bond remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)For classification, nomenclature, and the carbon–halogen bond, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Only the name of the substance is needed for classification, nomenclature, and the carbon–halogen bond; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(a) Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.

Halo compounds are classified by the carbon bearing halogen and number of halogens. The polar C–X bond, bond strength, hybridisation, resonance in haloarenes, and leaving-group ability control their nomenclature, physical behaviour, and reactivity.

Preparation of haloalkanes and haloarenes

Question 4

Which statement gives the correct Class XII chemistry for ‘Preparation of haloalkanes and haloarenes’?

  1. (a)The same conclusion about preparation of haloalkanes and haloarenes remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Only the name of the substance is needed for preparation of haloalkanes and haloarenes; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.
  4. (d)For preparation of haloalkanes and haloarenes, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(c) Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.

Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.

Question 5

Which idea should you remember when checking a conclusion about ‘Preparation of haloalkanes and haloarenes’?

  1. (a)Only the name of the substance is needed for preparation of haloalkanes and haloarenes; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  2. (b)For preparation of haloalkanes and haloarenes, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  3. (c)Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.
  4. (d)The same conclusion about preparation of haloalkanes and haloarenes remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
Show answer

(c) Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.

Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.

Question 6

Which statement correctly governs a new case involving preparation of haloalkanes and haloarenes?

  1. (a)The same conclusion about preparation of haloalkanes and haloarenes remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Only the name of the substance is needed for preparation of haloalkanes and haloarenes; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)For preparation of haloalkanes and haloarenes, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.
Show answer

(d) Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.

Haloalkanes arise from alcohol substitution, hydrocarbon halogenation, and addition routes, while haloarenes are prepared by electrophilic halogenation or diazonium replacement. Reagent and condition determine selectivity and by-products.

Nucleophilic substitution and stereochemistry

Question 7

Which statement gives the correct Class XII chemistry for ‘Nucleophilic substitution and stereochemistry’?

  1. (a)SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.
  2. (b)Only the name of the substance is needed for nucleophilic substitution and stereochemistry; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)The same conclusion about nucleophilic substitution and stereochemistry remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  4. (d)For nucleophilic substitution and stereochemistry, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(a) SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.

SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.

Question 8

Which idea should you remember when checking a conclusion about ‘Nucleophilic substitution and stereochemistry’?

  1. (a)For nucleophilic substitution and stereochemistry, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  2. (b)SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.
  3. (c)The same conclusion about nucleophilic substitution and stereochemistry remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  4. (d)Only the name of the substance is needed for nucleophilic substitution and stereochemistry; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(b) SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.

SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.

Question 9

Which statement correctly governs a new case involving nucleophilic substitution and stereochemistry?

  1. (a)For nucleophilic substitution and stereochemistry, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  2. (b)SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.
  3. (c)Only the name of the substance is needed for nucleophilic substitution and stereochemistry; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)The same conclusion about nucleophilic substitution and stereochemistry remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
Show answer

(b) SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.

SN2 substitution is one-step backside attack with inversion and is favoured by low steric hindrance; SN1 proceeds through a planar carbocation, is favoured by stable carbocations and polar protic media, and commonly gives racemisation with rearrangement possible.

Elimination, organometallic formation, and coupling

Question 10

Which statement gives the sound Class XII chemistry for ‘Elimination, organometallic formation, and coupling’?

  1. (a)Haloalkanes undergo elimination with alcoholic base, metal insertion to form Grignard reagents under dry conditions, and coupling reactions under specific metals. Substitution–elimination competition depends on substrate, base, solvent, and temperature.
  2. (b)Only the name of the substance is needed for elimination, organometallic formation, and coupling; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)For elimination, organometallic formation, and coupling, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)The same conclusion about elimination, organometallic formation, and coupling remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
Show answer

(a) Haloalkanes undergo elimination with alcoholic base, metal insertion to form Grignard reagents under dry conditions, and coupling reactions under specific metals. Substitution–elimination competition depends on substrate, base, solvent, and temperature.

Haloalkanes undergo elimination with alcoholic base, metal insertion to form Grignard reagents under dry conditions, and coupling reactions under specific metals. Substitution–elimination competition depends on substrate, base, solvent, and temperature.

Question 11

Which principle should be retained when checking an inference about ‘Elimination, organometallic formation, and coupling’?

  1. (a)Haloalkanes undergo elimination with alcoholic base, metal insertion to form Grignard reagents under dry conditions, and coupling reactions under specific metals. Substitution–elimination competition depends on substrate, base, solvent, and temperature.
  2. (b)Only the name of the substance is needed for elimination, organometallic formation, and coupling; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)For elimination, organometallic formation, and coupling, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)The same conclusion about elimination, organometallic formation, and coupling remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
Show answer

(a) Haloalkanes undergo elimination with alcoholic base, metal insertion to form Grignard reagents under dry conditions, and coupling reactions under specific metals. Substitution–elimination competition depends on substrate, base, solvent, and temperature.

Haloalkanes undergo elimination with alcoholic base, metal insertion to form Grignard reagents under dry conditions, and coupling reactions under specific metals. Substitution–elimination competition depends on substrate, base, solvent, and temperature.

Haloarene reactivity and orientation

Question 12

Which statement gives the sound Class XII chemistry for ‘Haloarene reactivity and orientation’?

  1. (a)Aryl C–X bonds are strengthened by resonance and sp2 character, hindering ordinary nucleophilic substitution. Halogen is deactivating yet ortho/para directing in electrophilic substitution; strong electron-withdrawing groups can activate nucleophilic aromatic substitution.
  2. (b)The same conclusion about haloarene reactivity and orientation remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)For haloarene reactivity and orientation, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Only the name of the substance is needed for haloarene reactivity and orientation; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(a) Aryl C–X bonds are strengthened by resonance and sp2 character, hindering ordinary nucleophilic substitution. Halogen is deactivating yet ortho/para directing in electrophilic substitution; strong electron-withdrawing groups can activate nucleophilic aromatic substitution.

Aryl C–X bonds are strengthened by resonance and sp2 character, hindering ordinary nucleophilic substitution. Halogen is deactivating yet ortho/para directing in electrophilic substitution; strong electron-withdrawing groups can activate nucleophilic aromatic substitution.

Question 13

Which principle should be retained when checking an inference about ‘Haloarene reactivity and orientation’?

  1. (a)The same conclusion about haloarene reactivity and orientation remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Aryl C–X bonds are strengthened by resonance and sp2 character, hindering ordinary nucleophilic substitution. Halogen is deactivating yet ortho/para directing in electrophilic substitution; strong electron-withdrawing groups can activate nucleophilic aromatic substitution.
  3. (c)For haloarene reactivity and orientation, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Only the name of the substance is needed for haloarene reactivity and orientation; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(b) Aryl C–X bonds are strengthened by resonance and sp2 character, hindering ordinary nucleophilic substitution. Halogen is deactivating yet ortho/para directing in electrophilic substitution; strong electron-withdrawing groups can activate nucleophilic aromatic substitution.

Aryl C–X bonds are strengthened by resonance and sp2 character, hindering ordinary nucleophilic substitution. Halogen is deactivating yet ortho/para directing in electrophilic substitution; strong electron-withdrawing groups can activate nucleophilic aromatic substitution.

Polyhalogen compounds and environmental effects

Question 14

Which statement gives the sound Class XII chemistry for ‘Polyhalogen compounds and environmental effects’?

  1. (a)Only the name of the substance is needed for polyhalogen compounds and environmental effects; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  2. (b)Polyhalogen compounds have specialised uses but may be persistent and harmful. Structure distinguishes dichloromethane, chloroform, iodoform, freons, and DDT; environmental conclusions must follow their stability, toxicity, and atmospheric chemistry.
  3. (c)The same conclusion about polyhalogen compounds and environmental effects remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  4. (d)For polyhalogen compounds and environmental effects, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(b) Polyhalogen compounds have specialised uses but may be persistent and harmful. Structure distinguishes dichloromethane, chloroform, iodoform, freons, and DDT; environmental conclusions must follow their stability, toxicity, and atmospheric chemistry.

Polyhalogen compounds have specialised uses but may be persistent and harmful. Structure distinguishes dichloromethane, chloroform, iodoform, freons, and DDT; environmental conclusions must follow their stability, toxicity, and atmospheric chemistry.

Question 15

Which principle should be retained when checking an inference about ‘Polyhalogen compounds and environmental effects’?

  1. (a)Polyhalogen compounds have specialised uses but may be persistent and harmful. Structure distinguishes dichloromethane, chloroform, iodoform, freons, and DDT; environmental conclusions must follow their stability, toxicity, and atmospheric chemistry.
  2. (b)The same conclusion about polyhalogen compounds and environmental effects remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)Only the name of the substance is needed for polyhalogen compounds and environmental effects; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)For polyhalogen compounds and environmental effects, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(a) Polyhalogen compounds have specialised uses but may be persistent and harmful. Structure distinguishes dichloromethane, chloroform, iodoform, freons, and DDT; environmental conclusions must follow their stability, toxicity, and atmospheric chemistry.

Polyhalogen compounds have specialised uses but may be persistent and harmful. Structure distinguishes dichloromethane, chloroform, iodoform, freons, and DDT; environmental conclusions must follow their stability, toxicity, and atmospheric chemistry.

Common misconception in Haloalkanes and Haloarenes

Open full misconception guide →

Should chlorobenzene react like chloroethane?

Wrong

Chlorobenzene readily substitutes chloride under the same conditions as chloroethane.

Why it feels right. Both contain a C–Cl bond and chloride seems like the same leaving group.

Right

Chlorobenzene has chlorine bonded to an aromatic sp² carbon. Resonance gives that C–Cl bond partial double-bond character.

Worked example

Chloroethane
C–Cl at saturated carbon→Can substitute under suitable mild conditions
Chlorobenzene
C–Cl at aromatic carbon→Much less reactive under those conditions
A C–Cl bond attached to an aromatic carbon behaves differently from one attached to a saturated carbon.
  1. Under mild conditions suitable for substituting chloroethane with aqueous hydroxide, chlorobenzene is much less reactive.
  2. Its aromatic C–Cl bond and geometry make the usual alkyl substitution pathways unfavourable.