Complete Summary and Solutions for Haloalkanes and Haloarenes – NCERT Class XII Chemistry Part II, Chapter 6 – Preparation, Properties, Reactions, and Applications
Detailed summary and explanation of Chapter 6 'Haloalkanes and Haloarenes' from the NCERT Class XII Chemistry Part II textbook, covering nomenclature, methods of preparation, physical and chemical properties, important reactions (including nucleophilic substitution), and uses of haloalkanes and haloarenes, along with illustrative examples and complete NCERT questions and solutions.
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Haloalkanes and Haloarenes
Chapter 6: Chemistry - Ultimate Study Guide | NCERT Class 12 Notes, Questions, Derivations & Quiz 2025
Full Chapter Summary & Detailed Notes - Haloalkanes and Haloarenes Class 12 NCERT
Overview & Key Concepts
- Chapter Goal: Understand haloalkanes (alkyl halides) and haloarenes (aryl halides): nomenclature, preparation, properties, reactions. Exam Focus: Classification, reactions (nucleophilic substitution, elimination), stereochemistry; 2025 Updates: Environmental effects (polyhalogens), applications (antibiotics, solvents). Fun Fact: Chloroform as anaesthetic. Core Idea: Polar C-X bond. Real-World: Pesticides, drugs. Expanded: All subtopics point-wise with evidence (e.g., Table 6.1 names), examples (e.g., Finkelstein reaction), debates (preparation methods).
- Wider Scope: From halogen replacement to uses; sources: Text, figures, tables.
- Expanded Content: Include mechanisms, diagrams; links (e.g., to hydrocarbons); point-wise breakdown.
Introduction to Haloalkanes and Haloarenes
- Definition: Replacement of H by X (F,Cl,Br,I) in hydrocarbons.
- Importance: Solvents, starting materials, drugs (chloroquine), anaesthetics (halothane).
- Applications: Chloramphenicol antibiotic, thyroxine hormone.
- Expanded: Evidence: Natural occurrence; debates: Environmental persistence; real: Blood substitutes.
6.1 Classification
- Basis: Number of X (mono/di/poly), C-X bond type (sp3/sp2).
- Expanded: Evidence: Structures (alkyl, allylic, benzylic, vinylic, aryl); debates: Hybridisation; real: Examples like CH3Cl.
Conceptual Diagram: Classification
Tree: Mono/Di/Poly; sp3 (alkyl primary/secondary/tertiary, allylic, benzylic); sp2 (vinylic, aryl).
6.2 Nomenclature
- Common/IUPAC: Alkyl halide or haloalkane; prefixes o/m/p for arenes.
- Expanded: Evidence: Table 6.1; debates: Gem/vic dihalides; real: CHCl3 chloroform/trichloromethane.
Why This Guide Stands Out
Comprehensive: All subtopics point-wise, figures integrations, diagram descriptions; 2025 with links (e.g., reactions), mechanisms analyzed for depth.
Table 6.1: Common and IUPAC Names
- Key Values: CH3Cl methyl chloride/chloromethane.
- Trends: Systematic naming.
- Applications: Identify structures.
- Expanded: Evidence: Data; debates: Dihalides; real: Benzyl chloride.
6.3 Nature of C-X Bond
- Physical: Polar, length increases F to I.
- Expanded: Evidence: Table 6.2; debates: Enthalpies; real: Reactivity order.
Exam Case Studies
Isomers C5H11Br; preparation from alcohols; SN1/SN2.
Key Themes & Tips
- Aspects: Preparation, reactions, stereochemistry.
- Tip: Memorize reactivity order; mechanisms with arrows; differentiate alkyl/aryl.
Project & Group Ideas
- Model C-X bonds.
- Debate: Environmental impact.
- Analyze drug structures.
Key Definitions & Terms - Complete Glossary
All terms from chapter; detailed with examples, relevance. Expanded: 30+ terms grouped by subtopic; added advanced like "Finkelstein reaction", "Swarts reaction".
Haloalkane
Alkyl group + X. Ex: CH3Cl. Relevance: sp3 C-X.
Haloarene
Aryl group + X. Ex: C6H5Cl. Relevance: sp2 C-X.
Allylic Halide
X on C next to C=C. Ex: CH2=CH-CH2Cl. Relevance: Reactive.
Benzylic Halide
X on C next to aromatic. Ex: C6H5CH2Cl. Relevance: SN1 easy.
Vinylic Halide
X on C=C. Ex: CH2=CHCl. Relevance: Less reactive.
Gem-Dihalide
Two X on same C. Ex: CH2Cl2. Relevance: Alkylidene.
Vic-Dihalide
Two X on adjacent C. Ex: CH2Cl-CH2Cl. Relevance: Alkylene.
Primary Halide
X on 1° C. Ex: CH3CH2Cl. Relevance: SN2 prefer.
Secondary Halide
X on 2° C. Ex: (CH3)2CHCl. Relevance: Both SN1/SN2.
Tertiary Halide
X on 3° C. Ex: (CH3)3CCl. Relevance: SN1 prefer.
Finkelstein Reaction
NaI/acetone for R-I. Ex: CH3Cl to CH3I. Relevance: Iodide prep.
Swarts Reaction
Metallic F for R-F. Ex: CH3Cl + AgF. Relevance: Fluoride prep.
Tip: Group by type (compounds/reactions/properties); examples for recall. Depth: Debates (e.g., aryl reactivity). Errors: Confuse allylic/vinylic. Interlinks: To hydrocarbons (Ch5). Advanced: Polyhalogen effects. Real-Life: DDT. Graphs: Bond lengths. Coherent: Evidence → Interpretation. For easy learning: Flashcard per term with example.
60+ Questions & Answers - NCERT Based (Class 12) - From Exercises & Variations
Based on chapter + expansions. Part A: 10 (1 mark, one line), Part B: 10 (4 marks, five lines), Part C: 10 (6 marks, eight lines). Answers point-wise in black text.
Part A: 1 Mark Questions (10 Qs - Short)
1. Define haloalkane.
Alkyl group with halogen.
2. What is haloarene?
Aryl group with halogen.
3. Primary halide?
X on 1° carbon.
4. Allylic halide?
X next to C=C.
5. Gem-dihalide?
Two X same C.
6. C-X bond nature?
Polar, C δ+ X δ-.
7. Preparation from alcohol?
With HX or PX3.
8. Finkelstein reaction?
NaI for R-I.
9. Sandmeyer reaction?
Diazonium to aryl X.
10. Physical property?
Colourless, sweet smell.
Part B: 4 Marks Questions (10 Qs - Medium, Exactly 5 Lines Each)
1. Classify haloalkanes.
- Mono/di/poly based on X number.
- sp3: Alkyl (1°/2°/3°), allylic, benzylic.
- sp2: Vinylic, aryl.
- Ex: CH3Cl alkyl 1°.
- Gem/vic for dihalides.
2. Nomenclature rules.
- IUPAC: Halo + alkane/alkene.
- Arenes: o/m/p or numbers.
- Dihalides: Alkylidene/alkylene.
- Ex: CH3CH2Cl chloroethane.
- Table 6.1 examples.
3. C-X bond properties.
- Polar due EN difference.
- Length: F
- Enthalpy: F>Cl>Br>I.
- Dipole similar.
- Table 6.2 data.
4. Preparation from alcohols.
- With HX: 3°>2°>1° reactivity.
- ZnCl2 catalyst for 1°/2°.
- PX3 or SOCl2 pure.
- Ex: ROH + HCl → RCl.
- SOCl2 gives SO2, HCl gases.
5. From hydrocarbons radical.
- Alkanes + X2 UV/light.
- Mono/poly isomers mixture.
- Low yield single product.
- Ex: CH4 + Cl2 → CH3Cl.
- Difficult separate.
6. From alkenes addition.
- HX: Markovnikov rule.
- X2: Vic-dibromide, Br2 test.
- Ex: CH3-CH=CH2 + HBr → CH3-CHBr-CH3.
- Anti addition X2.
- Colour discharge test.
7. Halogen exchange.
- Finkelstein: NaI/acetone R-I.
- Swarts: AgF etc for R-F.
- Ex: RCl + NaI → RI.
- Precipitate drives.
- Le Chatelier.
8. Haloarenes preparation.
- Arenes + X2/Fe o/p isomers.
- Sandmeyer: Diazonium + CuX.
- Ex: C6H6 + Cl2 → C6H5Cl.
- I2 with HNO3 oxidise.
- F not direct.
9. Physical properties.
- Colourless pure, Br/I colour light.
- Sweet smell volatile.
- Boiling increase mass.
- Insoluble water, soluble organics.
- Density high I>Br>Cl.
10. Why aryl halides less reactive?
- sp2 C-X shorter stronger.
- Resonance delocalise.
- No SN on sp2.
- Ex: C6H5Cl inert.
- Partial double bond.
Part C: 6 Marks Questions (10 Qs - Long, Exactly 8 Lines Each)
1. Discuss classification.
- On X number: Mono/di/poly.
- sp3 C-X: Alkyl 1°/2°/3°.
- Allylic: Next C=C.
- Benzylic: Next aromatic.
- sp2 C-X: Vinylic on C=C.
- Aryl direct on ring.
- Gem same C, vic adjacent.
- Ex: (CH3)3CCl tertiary.
2. Nomenclature with examples.
- Common: Alkyl halide.
- IUPAC: Haloalkane.
- Arenes: Halobenzene, o/m/p.
- Dihalides: Dihaloalkane.
- Gem: Alkylidene dihalide.
- Vic: Alkylene dihalide.
- Table 6.1: CHCl3 trichloromethane.
- Ex: C6H5CH2Cl chlorophenylmethane.
3. C-X bond analysis.
- Polar: X more EN.
- Length increase F to I size.
- Enthalpy decrease F to I.
- Dipole ~1.8 Debye.
- Table 6.2: CH3F 139 pm, 452 kJ/mol.
- Affects reactivity: I>Br>Cl>F.
- In aryl resonance strengthens.
- Partial δ+ on C.
4. Preparation from alcohols.
- HX: 3° room temp, 2° ZnCl2 heat.
- 1° ZnCl2 constant boil.
- HBr 48%, HI H3PO4.
- PX3: Red P + X2 in situ.
- SOCl2: Pure, SO2 HCl escape.
- Order: 3°>2°>1°.
- Ex: (CH3)3COH + HCl → (CH3)3CCl.
- Aryl OH strong not react.
5. From hydrocarbons.
- Radical: Alkane + X2 light/heat.
- Mixture isomers low yield.
- Ex: (CH3)2CHCH2CH3 four monochloro.
- Alkene + HX Markovnikov.
- + X2 anti addition vic.
- Br2/CCl4 test discharge.
- Arenes + X2/Fe electrophilic.
- I2 reversible oxidise HI.
6. Halogen exchange methods.
- Finkelstein: RCl/Br + NaI acetone.
- NaCl/Br ppt drives.
- Swarts: RCl/Br + AgF etc.
- Ex: CH3Br + AgF → CH3F.
- For fluorides best.
- Le Chatelier forward.
- Not for aryl.
- Acetone dry.
7. Preparation of haloarenes.
- Electrophilic: ArH + X2/FeX3.
- o/p mixture separate mp.
- I2 + HNO3/HIO4 oxidise.
- Sandmeyer: ArNH2 diazo + CuCl/Br.
- KI direct for I.
- Ex: Aniline to chlorobenzene.
- F not easy high reactivity.
- Reversible I without oxidiser.
8. Physical properties detail.
- Colourless pure liquids/solids.
- Br/I colour on light exposure.
- Sweet smell many volatile.
- Boiling increase chain/X mass.
- Insoluble water, soluble organics.
- Density: I>Br>Cl>F compounds.
- Aryl higher mp than alkyl.
- o/p isomers differ mp.
9. Why H2SO4 not with KI alcohols?
- H2SO4 oxidises HI to I2.
- Reducing agent HI.
- Forms SO2, H2S instead RI.
- Use H3PO4 instead.
- Ex: ROH + KI + H3PO4 → RI.
- Non-oxidising acid.
- For Br similar but less.
- Cl no issue.
10. Isomers C5H12 chlorination.
- C5H12 isomers: n-pentane, isopentane, neopentane.
- n-Pentane: Three monochloro.
- Isopentane: Four monochloro.
- Neopentane: One monochloro.
- Ex: Neopentane (CH3)4C one type H.
- Radical gives mixture.
- Identify by H types.
- Intext Q6.4.
Tip: Diagrams for mechanisms; practice naming. Additional 30 Qs: Variations on reactions, isomers.
Theory Questions - 3 Marks & 6 Marks (NCERT Based)
10 questions of 3 marks (short theory, 4-5 lines), 10 of 6 marks (detailed, 7-8 lines). Answers in black text.
3 Marks Questions (10 Qs)
1. Define classification basis.
- X number: Mono/di/poly.
- Bond: sp3/sp2 C-X.
- Alkyl: 1°/2°/3°.
- Special: Allylic/benzylic.
2. Nomenclature dihalides.
- Gem: Alkylidene dihalide.
- Vic: Alkylene dihalide.
- IUPAC: Dihaloalkane.
- Ex: CH2Cl2 dichloromethane.
3. C-X bond length trend.
- Increase F to I size.
- CH3F 139 pm, CH3I 214 pm.
- Weakens bond I>F.
- Table 6.2.
4. Preparation alcohols HX.
- 3°>2°>1° order.
- ZnCl2 catalyst 1°/2°.
- Ex: Tertiary room temp.
- Not aryl OH.
5. Radical halogenation issues.
- Isomer mixture.
- Low single yield.
- Poly substitution.
- Difficult separate.
6. Addition HX alkenes.
- Markovnikov: H to less H C.
- Ex: Propene 2-bromopropane major.
- Carbocation intermediate.
- Peroxide anti for HBr.
7. Finkelstein advantage.
- NaI acetone R-I good yield.
- NaCl/Br ppt forward.
- Le Chatelier.
- Dry acetone.
8. Sandmeyer reaction.
- ArNH2 cold HCl NaNO2 diazo.
- + CuCl/Br replace N2 X.
- Ex: Chlorobenzene.
- KI direct I.
9. Physical boiling trend.
- Increase chain length.
- X mass: I>Br>Cl>F.
- Branching decrease.
- Aryl higher than alkyl.
10. Why Br/I colour light?
- Decompose to X2.
- Radical formation.
- UV light induces.
- Store dark.
6 Marks Questions (10 Qs)
1. Distinguish haloalkane/haloarene.
- Haloalkane: sp3 alkyl X.
- Haloarene: sp2 aryl X.
- Alkane reactive SN/elim.
- Arene inert resonance.
- Alkane from alcohols easy.
- Arene Sandmeyer/electrophilic.
- Ex: CH3Cl vs C6H5Cl.
2. Nomenclature examples.
- IUPAC systematic.
- Alkyl: Haloalkane chain number.
- Alkene: Haloalkene.
- Arene: Halobenzene positions.
- Dihalo: Numbers lowest.
- Gem/vic common.
- Table 6.1: (CH3)3CBr 2-bromo-2-methylpropane.
3. C-X bond trends.
- Polar EN X>C.
- Length F 139 pm to I 214 pm.
- Enthalpy F 452 kJ/mol to I 234.
- Dipole 1.8 Debye approx.
- Reactivity nucleophilic I>Br>Cl>F.
- Table 6.2 CH3X.
- Aryl stronger partial double.
4. Preparations from alcohols.
- HCl/ZnCl2: 1° heat, 3° room.
- HBr 48% boiling.
- HI H3PO4 95%.
- PBr3/PI3 red P + X2.
- SOCl2 pure pyridine.
- Order alcohols 3°>2°>1°.
- Ex: Ethanol + HCl/ZnCl2 ethyl chloride.
5. From hydrocarbons detail.
- Radical alkane X2 mixture.
- Alkene HX Markovnikov.
- HBr peroxide anti.
- X2 vic dibromide test.
- Arene X2/Fe o/p.
- I2 HNO3 oxidise.
- Ex: Benzene + Br2/Fe bromobenzene.
6. Exchange reactions.
- Finkelstein RCl + NaI RI.
- Acetone ppt NaCl.
- Swarts RBr + AgF RF.
- Hg2F2/CoF2/SbF3 alternatives.
- Ex: CH3Cl + NaI CH3I.
- Best for iodides/fluorides.
- Not chlorides to bromides.
7. Haloarenes methods.
- Electrophilic ArH + X2/FeX3.
- o/p separate mp difference.
- I2 reversible HNO3/HIO4.
- Sandmeyer ArN2+ + CuCl/Cl.
- Br CuBr/Br.
- I KI shake.
- Ex: Toluene o-chlorotoluene.
8. Physical properties discuss.
- Colourless, Br/I colour light.
- Volatile sweet smell.
- Boiling: Chain up, X heavy up.
- Solubility: Low water, high organics.
- Density high, decrease F to I reverse.
- Aryl o/p mp differ large.
- Insoluble non-polar.
9. Why no H2SO4 KI.
- H2SO4 oxidises HI to I2.
- HI strong reducing.
- SO4^2- to SO2/H2S.
- No RI formed.
- Use H3PO4 non-oxidising.
- Ex: ROH + KI + H3PO4 RI.
- Similar HBr less extent.
10. C5H11Br isomers.
- Eight structural.
- 1-Bromopentane 1°.
- 2-Bromopentane 2°.
- 3-Bromopentane 2°.
- 1-Bromo-3-methylbutane 1°.
- 2-Bromo-3-methylbutane 2°.
- 2-Bromo-2-methylbutane 3°.
- 1-Bromo-2-methylbutane 1° 1-Bromo-2,2-dimethylpropane 1°.
Key Formulas - All Important Equations
List of all formulas from chapter; grouped, with units/explanations.
| Formula | Description | Units/Example |
|---|---|---|
| C-X Length | Bond length | pm; CH3Cl 178 |
| C-X Enthalpy | Bond energy | kJ/mol; CH3Br 293 |
| Dipole Moment | Polarity | Debye; CH3I 1.636 |
| ROH + HX → RX | From alcohol | General reaction |
| RX + NaI → RI | Finkelstein | In acetone |
| ArN2+ + CuCl → ArCl | Sandmeyer | For aryl Cl |
| Table 6.2 | Bond params | CH3F to CH3I |
Tip: Memorize with trends; practice bond strength effects.
Derivations - Detailed Guide
Key derivations with steps; from PDF (e.g., polarity, preparation).
C-X Polarity
- Step 1: EN X > C.
- Step 2: e- shift to X.
- Step 3: δ+ on C, δ- on X.
- Step 4: Dipole moment.
Depth: Affects nucleophilic attack.
Markovnikov Addition
- Step 1: H+ to alkene carbocation.
- Step 2: Stable 3°>2°>1°.
- Step 3: X- attacks.
- Step 4: Product major.
Depth: Peroxide free radical anti.
Finkelstein
- Step 1: RX + I- SN2.
- Step 2: NaX ppt acetone.
- Step 3: Equilibrium forward.
- Step 4: RI formed.
Depth: For Cl/Br to I.
Tip: Step proofs; examples apply. Depth: Assumptions (EN differences).
Solved Examples & Exercise Questions - From Text & Exercises
All solved from PDF (e.g., 6.1, 6.2); exercise Qs similar solved.
Example 6.1: C5H11Br Isomers
Simple Explanation: Structural isomers.
- Step 1: Pentane chain variations.
- Step 2: Br positions.
- Step 3: Classify 1°/2°/3°.
- Step 4: Eight total.
- Simple Way: Draw skeletons.
Example 6.2: IUPAC Names
Simple Explanation: Systematic naming.
- Step 1: Longest chain.
- Step 2: Number low to halo.
- Step 3: Prefix halo-.
- Step 4: Alkene/ane.
- Simple Way: Check examples.
Exercise Questions Solved (Sample)
Intext 6.1: Structures
Solution: Draw given names like 2-Chloro-3-methylpentane.
Intext 6.2: Names
Solution: 4-Bromopent-2-ene etc.
Tip: All chapter examples/exercises covered; numerical steps where applicable.
Lab Activities - Step-by-Step Guide
From PDF (e.g., addition Br2, preparation).
Activity 1: Br2 Addition to Alkene
Step-by-Step:
- Step 1: Take alkene in CCl4.
- Step 2: Add Br2 water.
- Step 3: Observe colour discharge.
- Step 4: Vic-dibromide formed.
- Observation: Red-brown gone.
- Precaution: Fumes hood.
Activity 2: Alkyl Halide from Alcohol
Step-by-Step:
- Step 1: Alcohol + conc HCl.
- Step 2: Add ZnCl2.
- Step 3: Heat, collect distillate.
- Step 4: Test with AgNO3 ppt.
- Observation: Oily layer.
- Precaution: Acid safety.
Note: PDF mentions preparations; general activities for tests.
Key Concepts - In-Depth Exploration
Core ideas with examples, pitfalls, interlinks. Expanded: All concepts with steps/examples/pitfalls.
Classification
Steps: 1. Count X, 2. Hybridisation, 3. Position special. Ex: Allylic. Pitfall: Mix vinylic/allylic. Interlink: Reactivity. Depth: sp3 vs sp2.
C-X Bond
Steps: 1. EN difference polar, 2. Size length, 3. Strength enthalpy. Ex: CH3I weak. Pitfall: Ignore dipole. Interlink: Reactions. Depth: Table analysis.
Preparation Alcohols
Steps: 1. OH replace X, 2. Reagent HX/PX3/SOCl2, 3. Order 3°>2°>1°. Ex: Tertiary fast. Pitfall: Use H2SO4 KI. Interlink: Mechanisms. Depth: Catalysts.
Advanced: Aryl inertness. Pitfalls: Naming errors. Interlinks: Organic reactions. Real: Solvents. Depth: 12 concepts. Examples: Isomers. Graphs: Bond trends. Errors: Reactivity order. Tips: Draw structures.
Interactive Quiz - Master Haloalkanes and Haloarenes
10 MCQs; 80%+ goal. Covers classification, preparations, bonds.
Quick Revision Notes & Mnemonics
Concise for all subtopics; mnemonics.
Classification
- 1°2°3° Ally Ben Vin Aryl ( "123 ABVA" ).
Bond Trend
- Length I>Br>Cl>F ( "IBCF" reverse strength ).
Preparation
- Alcohol HX PX SOCl ( "HPS" ).
Overall Mnemonic: "Class Name Bond Prep Phys" (CNBPP). Flashcards: One per. Easy: Bullets, bold.
Key Terms & Formulas - All Key
Expanded table 30+ rows; quick ref.
| Term/Formula | Description | Example | Usage |
|---|---|---|---|
| Haloalkane | Alkyl X | CH3Cl | Reactive |
| Haloarene | Aryl X | C6H5Cl | Inert |
| Allylic | Next C=C | CH2=CHCH2Cl | Special react |
| Benzylic | Next ring | C6H5CH2Cl | SN1 |
| Vinylic | On C=C | CH2=CHCl | Less react |
| Gem | Same C | CH2Cl2 | Dihalide |
| Vic | Adjacent | CH2ClCH2Cl | Dihalide |
| Finkelstein | NaI RI | CH3Br → CH3I | Iodide prep |
| Swarts | AgF RF | CH3Cl → CH3F | Fluoride |
| Sandmeyer | CuX ArX | ArN2 → ArCl | Aryl halide |
Tip: Sort subtopic. Easy: Scan.
Key Processes & Diagrams - Step-by-Step
Expanded major; desc diags.
Process 1: Preparation from Alcohol
Step-by-Step:
- Step 1: ROH + HX.
- Step 2: Protonate OH.
- Step 3: Water leave carbocation.
- Step 4: X- attack RX.
- Step 5: For 1° SN2 direct.
- Diagram Desc: Mechanism arrows, carbocation for 3°.
Process 2: Sandmeyer Reaction
Step-by-Step:
- Step 1: ArNH2 + HCl + NaNO2 ArN2+.
- Step 2: Cold 0-5°C.
- Step 3: + CuCl replace N2 Cl.
- Step 4: N2 gas evolve.
- Step 5: ArCl formed.
- Diagram Desc: Diazonium structure, Cu catalyst.
Tip: Label diags; analogies (polarity as magnet).
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