Haloarenes
Class 12 Chemistry Notes • NEB Syllabus 2083
Syllabus, 15 solved multiple choice questions, 7 short and 7 long answer questions with structures drawn for every reaction, handwritten and typed PDF notes and frequently asked questions on the preparation, properties and uses of haloarenes.
1. Syllabus
Unit 9: Haloarenes
These notes follow the NEB Class 12 Chemistry syllabus (+2 Chemistry, Nepal). Practise the multiple choice questions first, then work through the solved short and long answer questions, and finish with the PDF notes for quick revision.
2. Multiple Choice Questions
- a) It has higher molecular weight
- b) It forms hydrogen bonds
- c) It has hydrogen bonds
- d) It is more reactive than benzene
Correct Answer: a) It has higher molecular weight
Reason: Chlorobenzene (boiling point \(132^\circ C\)) is heavier than benzene (\(80^\circ C\)), so its London dispersion forces are stronger. It is also polar because of the \(C-Cl\) bond, so there are dipole-dipole forces as well. Chlorobenzene has no \(O-H\) or \(N-H\) bond, so it cannot form hydrogen bonds, and reactivity has no relation with boiling point.
- a) \(para>ortho>meta\)
- b) \(meta>ortho>para\)
- c) \(ortho>meta>para\)
- d) \(para>meta>ortho\)
Correct Answer: c) \(ortho>meta>para\)
Reason: The question deals with the isomers of dichlorobenzene (\(C_6H_4Cl_2\)). The ortho isomer has the highest dipole moment, so the dipole-dipole attraction is strongest and its boiling point (about \(180^\circ C\)) is the highest. The meta and para isomers boil at nearly the same lower temperature (about \(173\) and \(174^\circ C\)), and the para isomer is non-polar. Among the given options only option c puts the ortho isomer at the top, so it is the answer of the textbook. (Note that the signs in the options show the order from the highest to the lowest.)
- a) \(Zn/HCl\)
- b) \(CuCl\) and \(HCl\)
- c) \(NaOH\) and \(Br_2\)
- d) \(SOCl_2\)
Correct Answer: b) \(CuCl\) and \(HCl\)
Reason: When benzene diazonium chloride is treated with cuprous chloride in hydrochloric acid the diazonium group is replaced by chlorine and nitrogen is evolved. This is the Sandmeyer reaction: \(C_6H_5N_2Cl\xrightarrow{CuCl/HCl}C_6H_5Cl+N_2\).
Figure: Sandmeyer reaction
- a) \(CH_3Cl\)
- b) \(C_6H_5Cl\)
- c) \(C_6H_5CH_2Cl\)
- d) \(CH_3I\)
Correct Answer: b) \(C_6H_5Cl\)
Reason: Chlorobenzene is a haloarene. The lone pair of chlorine is in resonance with the ring, so the \(C-Cl\) bond gets a partial double bond character, and the carbon is \(sp^2\) hybridised. The bond is strong, so nucleophilic substitution does not take place easily. \(CH_3Cl\), \(C_6H_5CH_2Cl\) and \(CH_3I\) are alkyl halides, which react readily.
- a) The carbon hydrogen bond in haloarenes is weaker than haloalkanes.
- b) The carbon in haloarenes have \(sp^3\) hybridization
- c) Resonance stabilization in haloarenes makes \(C-X\) bond stronger.
- d) The halogen in haloarenes is more reactive than in haloalkanes.
Correct Answer: c) Resonance stabilization in haloarenes makes \(C-X\) bond stronger.
Reason: The lone pair of the halogen is delocalised into the benzene ring, which gives the \(C-X\) bond a partial double bond character (it becomes shorter and stronger). The carbon of a haloarene is \(sp^2\) hybridised, not \(sp^3\), and this also strengthens the bond.
- a) It increases electron density at all positions
- b) It decreases electron density at ortho and para positions.
- c) It decreases electron density at meta position.
- d) It increases electron density at ortho and para position.
Correct Answer: d) It increases electron density at ortho and para position.
Reason: The lone pair of the halogen is donated to the ring (\(+M\) effect), and this puts a partial negative charge on the ortho and para carbons (see the resonating structures). The ring as a whole is less electron-rich than benzene because of the stronger \(-I\) effect, but the ortho and para positions have more electron density than the meta position, so the electrophile enters there.
- a) \(+I\) effect of halogen.
- b) \(-I\) and \(+M\) effect respectively
- c) Only \(-I\) effect of halogen.
- d) Only \(+M\) effect of halogens.
Correct Answer: b) \(-I\) and \(+M\) effect respectively
Reason: The halogen is highly electronegative, so it withdraws electrons through the sigma bond (\(-I\) effect), and the ring becomes less reactive (deactivated). But its lone pair is donated by resonance (\(+M\) effect) and this increases the electron density at the ortho and para positions, so it directs the incoming group there.
- a) Chlorobenzene and benzene.
- b) Chlorobenzene and chloral
- c) Benzene and chloral.
- d) Chlorobenzene and chloritone
Correct Answer: b) Chlorobenzene and chloral
Reason: Two molecules of chlorobenzene condense with one molecule of chloral (\(CCl_3CHO\)) in presence of conc. \(H_2SO_4\) to give DDT and water: \(2C_6H_5Cl+CCl_3CHO\xrightarrow{conc.\,H_2SO_4}(ClC_6H_4)_2CH\text{-}CCl_3+H_2O\).
- a) The chlorine atom activates the ring for substitution.
- b) The chlorine atom deactivates the ring and makes it less reactive.
- c) The chlorine atom undergoes nucleophilic substitution.
- d) The chlorine atom doesnot affect the reaction.
Correct Answer: b) The chlorine atom deactivates the ring and makes it less reactive.
Reason: The strong \(-I\) effect of chlorine withdraws electron density from the ring, so the ring is less reactive towards the electrophile (the carbocation) than benzene, and the reaction is slow and the yield is poor.
- a) Wurtz reaction.
- b) Friedel-Crafts alkylation
- c) Sandmeyer reaction.
- d) Williamson’s ether synthesis
Correct Answer: c) Sandmeyer reaction.
Reason: In the Sandmeyer reaction a diazonium salt is changed to an aryl halide with \(CuCl\) or \(CuBr\). The Wurtz reaction forms alkanes, Friedel-Crafts alkylation forms alkylbenzenes and Williamson’s synthesis forms ethers.
- a) Toluene.
- b) Biphenyl
- c) Benzophenone.
- d) Benzyl chloride
Correct Answer: b) Biphenyl
Reason: Two molecules of chlorobenzene couple in the presence of sodium and dry ether to form biphenyl (diphenyl): \(2C_6H_5Cl+2Na\xrightarrow{dry\,ether}C_6H_5-C_6H_5+2NaCl\).
Figure: Fittig reaction
- a) \(o-\)nitrochlorobenzene.
- b) \(m-\)nitrochlorobenzene
- c) \(p-\)nitrochlorobenzene.
- d) Both o-and p- nitrochlorobenzene
Correct Answer: c) \(p-\)nitrochlorobenzene.
Reason: Chlorine directs the nitro group to the ortho and para positions, so very little meta product is formed. The para isomer is the major product (the textbook figure shows 2- and 4-chloronitrobenzene), because the ortho position is crowded by the chlorine atom (steric hindrance).
Figure: Nitration of chlorobenzene
- a) Benzyl chloride.
- b) Chlorobenzene
- c) Methyl chloride.
- d) Allyl chloride
Correct Answer: b) Chlorobenzene
Reason: In chlorobenzene the \(C-Cl\) bond is strong (resonance, \(sp^2\) carbon). Benzyl chloride, allyl chloride and methyl chloride have the halogen on a \(sp^3\) carbon, and benzyl and allyl chlorides even give stable carbocations, so they react readily.
- a) Kolbe’s reaction.
- b) Fittig reaction
- c) Reimer-Teimann reaction.
- d) Wurtz reaction
Correct Answer: c) Reimer-Teimann reaction.
Reason: In the Reimer-Tiemann reaction, the dichlorocarbene (\(:CCl_2\), an electrophile) attacks the phenoxide ring (electrophilic substitution), and then the \(Cl\) atoms of the \(-CHCl_2\) group are replaced by \(OH^-\) (nucleophilic substitution), giving the aldehyde after loss of water. Kolbe’s reaction is electrophilic only, and Fittig and Wurtz are coupling reactions of sodium.
- a) Water helps in stabilizing the product.
- b) Dry ether prevents oxidation of sodium
- c) Sodium reacts violently with water and can demolish the reaction.
- d) Ether acts as an oxidizing agent.
Correct Answer: c) Sodium reacts violently with water and can demolish the reaction.
Reason: Sodium reacts violently with water (\(2Na+2H_2O\rightarrow2NaOH+H_2\)), so the sodium is used up and the reaction fails. The reaction must be carried out in an anhydrous (dry) solvent such as ether, which dissolves the halide and does not react with sodium.
3. Numerical and Subjective Questions
Short Answer Questions
Figure: Three isomers of dichlorobenzene
The molecular formula \(C_6H_4Cl_2\) is dichlorobenzene. The benzene ring has two hydrogens replaced by two chlorine atoms, and three positional (position) isomers are possible, because the two chlorines can be placed at the ortho (1,2), meta (1,3) or para (1,4) positions:
| Isomer | IUPAC name | Common name | Nature |
|---|---|---|---|
| I | 1,2-Dichlorobenzene | o-Dichlorobenzene | Polar (highest boiling point) |
| II | 1,3-Dichlorobenzene | m-Dichlorobenzene | Polar |
| III | 1,4-Dichlorobenzene | p-Dichlorobenzene | Non-polar, symmetrical (highest melting point) |
The para isomer has the highest melting point because its symmetrical structure packs well in the crystal.
i) What happens when benzene is treated with chlorine?
Figure: Direct chlorination of benzene
When dry chlorine is passed through benzene in the presence of anhydrous \(FeCl_3\) (or \(AlCl_3\)) as a halogen carrier in the dark, a hydrogen atom of the ring is replaced by chlorine and chlorobenzene is formed. It is an electrophilic aromatic substitution reaction: \(Cl_2+FeCl_3\rightarrow Cl^++FeCl_4^-\), and \(Cl^+\) attacks the ring. \(C_6H_6+Cl_2\xrightarrow{FeCl_3}C_6H_5Cl+HCl\).
ii) How will you prepare chlorobenzene from benzene diazonium chloride? Name the reaction.
Figure: Aniline to chlorobenzene (diazotisation followed by Sandmeyer reaction)
Aniline is dissolved in cold aqueous hydrochloric acid and treated with sodium nitrite at \(0-5^\circ C\) to give benzene diazonium chloride. When this is warmed with cuprous chloride in hydrochloric acid the diazonium group is replaced by chlorine and nitrogen escapes. The reaction is the Sandmeyer reaction:
If copper powder and \(HCl\) are used in place of \(CuCl\), the reaction is called the Gattermann reaction (a modification of the Sandmeyer reaction).
iii) What is the use of CuCl in the preparation of chlorobenzene from diazonium chloride?
\(CuCl\) works as a catalyst. \(Cu(I)\) gives an electron to the diazonium ion, so nitrogen is released and a phenyl radical is formed. The copper then passes a chlorine atom to the phenyl radical to give chlorobenzene, and \(CuCl\) is regenerated. It also supplies the chloride needed for the substitution of the diazonium group.
i) Compare the solubility of chlorobenzene in water and organic solvent.
Chlorobenzene is insoluble in water but it is readily soluble in organic solvents like benzene, ether and alcohol. It cannot form hydrogen bonds with water and its large non-polar benzene ring is hydrophobic, so the water molecules (which are strongly hydrogen bonded to each other) do not mix with it. In organic solvents the attraction between the molecules is of the same kind, so they dissolve. It is heavier than water (density 1.11 g/cc), and it sinks.
ii) Arrange the following in the increasing order of boiling point. Chlorobenzene, Bromobenzene and Iodobenzene
Chlorobenzene < Bromobenzene < Iodobenzene (about \(132^\circ C\), \(156^\circ C\) and \(188^\circ C\)). The size and the mass of the halogen increase in the order \(Cl<Br<I\), so the van der Waals (dispersion) forces between the molecules increase, and more energy is needed to separate them.
iii) What is the reason behind higher boiling point of chlorobenzene than that of benzene?
Benzene is non-polar and has only weak London dispersion forces. Chlorobenzene has a higher molecular mass, so its dispersion forces are stronger, and it also has a permanent dipole because of the polar \(C-Cl\) bond, so there are dipole-dipole attractions between its molecules. So its boiling point (\(132^\circ C\)) is higher than that of benzene (\(80^\circ C\)).
i) \(C_6H_5Cl+Conc.H_2SO_4\xrightarrow{Conc.HNO_3}\)
Figure: Nitration
Nitration. The major product is 4-chloronitrobenzene (p-chloronitrobenzene), with 2-chloronitrobenzene as the minor product.
ii) \(C_6H_5Cl+Conc.H_2SO_4\xrightarrow{\Delta}\)
Figure: Sulphonation
Sulphonation. The major product is 4-chlorobenzenesulphonic acid.
iii) \(C_6H_5Cl+CH_3COCl\xrightarrow{anhy.AlCl_3}\)
Figure: Friedel-Crafts acylation
Friedel-Crafts acylation. The major product is 4-chloroacetophenone (p-chloroacetophenone).
iv) \(C_6H_5Cl+CH_3Cl\xrightarrow{anhy.AlCl_3}\)
Figure: Friedel-Crafts alkylation
Friedel-Crafts alkylation. The major product is 4-chlorotoluene (p-chlorotoluene).
v) \(C_6H_5Cl+Cl_2\xrightarrow{FeCl_3}\)
Figure: Chlorination
Halogenation (the textbook prints \(Cl_4\), which is a misprint of \(Cl_2\)). The major product is 1,4-dichlorobenzene (p-dichlorobenzene).
In all these reactions the chlorine is an ortho-para director, so the substituent goes to the ortho and para positions, and the para isomer is the major product because of less steric hindrance. The reactions are slower than those of benzene, because chlorine deactivates the ring.
i) \(C_6H_5Cl+H_2\xrightarrow{Ni,\Delta}\)
Figure: Reduction of chlorobenzene
ii) \(C_6H_5Cl\xrightarrow{Na,\ C_2H_5OH}\)
Sodium and ethanol give nascent hydrogen, which reduces chlorobenzene to benzene:
iii) \(C_6H_5Cl\xrightarrow{Zn,\ NaOH}\)
Zinc and sodium hydroxide give nascent hydrogen (like the \(Ni-Al/NaOH\) reduction in the book), which reduces chlorobenzene to benzene:
iv) \(C_6H_5Cl\xrightarrow{Na,\ dry\ ether}\)
Figure: Fittig reaction
Fittig reaction: \(2C_6H_5Cl+2Na\xrightarrow{dry\,ether}C_6H_5-C_6H_5\ (\text{biphenyl})+2NaCl\).
v) \(C_6H_5Cl+CH_3Cl\xrightarrow{Na,\ dry\ ether}\)
Figure: Wurtz-Fittig reaction
Wurtz-Fittig reaction: \(C_6H_5Cl+CH_3Cl+2Na\xrightarrow{dry\,ether}C_6H_5CH_3\ (\text{toluene})+2NaCl\).
Polychlorinated biphenyls (PCBs) are biphenyl molecules in which many hydrogens are replaced by chlorine. They were used as coolants and insulating fluids in transformers and capacitors, because they are chemically inert and do not burn easily. The same stability is the reason for the ban:
1. They are not broken down by sunlight, water, microbes or chemicals, so they remain in the soil, water and air for decades (persistent organic pollutants).
2. They are fat soluble and not water soluble, so they accumulate in the fatty tissue of animals and become more concentrated at each step of the food chain (bioaccumulation and biomagnification).
3. They are toxic: they damage the liver, the nervous, immune and endocrine (hormone) systems, and cause cancer in humans and animals.
i) Benzene diazonium chloride, Cu/HBr
Figure: Gattermann reaction
Bromobenzene is formed, and the reaction is the Gattermann reaction (copper powder with the halogen acid). With \(CuBr/HBr\) it is the Sandmeyer reaction.
ii) Benzene diazonium chloride, CuCl/HCl
Figure: Sandmeyer reaction
Chlorobenzene is formed (Sandmeyer reaction).
Long Answer Questions
i) Explain the reason behind less reactivity of haloarene towards nucleophilic substitution reaction.
Figure: Resonating structures of chlorobenzene (negative charge at ortho and para positions)
Haloarenes are much less reactive than haloalkanes towards nucleophilic substitution because of:
1. Resonance effect: the lone pair of the halogen is delocalised into the ring, so chlorobenzene is a resonance hybrid of the above structures. In structures II, III and IV the carbon and the halogen are joined by a double bond (the halogen has partial positive charge), so the \(C-X\) bond has a partial double bond character. It is shorter and stronger, and it is difficult to replace the halogen. This situation does not occur in haloalkanes.
2. Hybridization: the carbon attached to the halogen in a haloarene is \(sp^2\) hybridised, which has more s-character (about 33%) than \(sp^3\) (25%), so it is more electronegative and holds the bonding pair of the \(C-X\) bond more tightly.
3. Electron-rich ring: the aryl group has a cloud of \(\pi\) electrons, which repels the incoming nucleophile (also an electron-rich species).
4. Unstable phenyl cation: if the halogen leaves as halide, the phenyl cation formed is not stabilised by resonance (its empty orbital is in the plane of the ring), so an \(S_N1\) path is not possible.
ii) Compare the bond strength of C-Cl bond and reactivity of haloarene and haloalkane towards nucleophilic substitution reaction.
| Basis | Haloalkane (e.g. CH₃Cl) | Haloarene (e.g. C₆H₅Cl) |
|---|---|---|
| Hybridization of C | sp³ | sp² |
| Nature of C-Cl bond | Pure single bond | Partial double bond (resonance) |
| C-Cl bond length | About 178 pm | About 169 pm (shorter) |
| C-Cl bond strength | Weaker | Stronger |
| Nucleophilic substitution | Easy, under mild conditions | Very difficult, needs drastic conditions |
So the \(C-Cl\) bond in chlorobenzene is shorter and stronger, and haloalkanes are far more reactive. Haloarenes react only under drastic (special) conditions, for example:
Figure: Dow’s process
i) How could you prove that -Cl is ortho and para director in chlorobenzene?
Figure: Resonating structures of chlorobenzene (negative charge at ortho and para positions)
When the lone pair of chlorine is donated into the ring (\(+M\) effect), the resonating structures II, III and IV show a negative charge on the ortho and para carbons only (structures with the charge on the meta carbon are not possible). So the electron density is highest at the ortho and para positions, and the incoming electrophile attacks these positions.
Experimental proof: on nitration, sulphonation, halogenation and Friedel-Crafts reactions chlorobenzene gives only the ortho and para products (for example 2- and 4-chloronitrobenzene), and no meta product is obtained. The para isomer is major, due to less steric hindrance.
Figure: Nitration of chlorobenzene
ii) In spite of being ortho-para director -Cl is deactivator of aromatic ring. Explain.
Chlorine has two opposing effects on the ring:
1. \(-I\) effect: chlorine is very electronegative, so it pulls electrons from the ring through the sigma bond, and this makes the whole ring less electron-rich.
2. \(+M\) effect: the lone pair of chlorine is donated to the ring by resonance, and this increases the electron density at the ortho and para positions.
For halogens the \(-I\) effect is stronger than the \(+M\) effect, so on the whole the ring has less electron density than benzene, and it is less reactive (deactivated) towards electrophilic substitution, so the reactions of chlorobenzene are slower than those of benzene. But the \(+M\) effect still operates at the ortho and para positions and stabilises the intermediate formed by attack at these positions, so the incoming group goes to the ortho and para positions. So \(-Cl\) is a deactivating but ortho-para directing group.
i) What happens when chlorobenzene is treated with chloroethane in presence of sodium and dry ether. Name the reaction.
Figure: Wurtz-Fittig reaction of chlorobenzene with chloroethane
Ethylbenzene is formed. The reaction is called the Wurtz-Fittig reaction.
ii) Compare Fittig and Wurtz-Fittig reactions with suitable examples.
| Basis | Fittig reaction | Wurtz-Fittig reaction |
|---|---|---|
| Reactants | Two molecules of an aryl halide | One aryl halide and one alkyl halide |
| Reagent | Sodium in dry ether | Sodium in dry ether |
| Product | Biaryl (diphenyl) | Alkylarene (alkylbenzene) |
| Example | \(2C_6H_5Cl+2Na\rightarrow C_6H_5-C_6H_5+2NaCl\) | \(C_6H_5Cl+CH_3Cl+2Na\rightarrow C_6H_5CH_3+2NaCl\) |
| Name of product in example | Biphenyl (phenylbenzene) | Toluene |
Figure: Fittig reaction
In the Wurtz-Fittig reaction, some biphenyl and alkane (from coupling of two alkyl halides) are also formed as side products. Dry ether is needed because sodium reacts violently with water.
i) What is the full form of DDT? Write structure and IUPAC name of the compound.
Figure: Structure of DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane)
DDT is Dichlorodiphenyltrichloroethane. Its IUPAC name is 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, \((ClC_6H_4)_2CH-CCl_3\).
ii) What happens when chlorobenzene is treated with chloral in presence of H₂SO₄.
Two molecules of chlorobenzene condense with one molecule of chloral (trichloroacetaldehyde, \(CCl_3CHO\)) in presence of conc. \(H_2SO_4\) (a dehydrating agent), and one molecule of water is eliminated. The para hydrogen of each chlorobenzene ring combines with the oxygen of the carbonyl group:
iii) Why the product of above reaction is used as insecticide?
DDT is very toxic to insects. It is fat soluble, so it enters the body of the insect through its waxy outer covering, and it acts on the nerve cells by keeping the sodium channels open, so the nerves fire repeatedly, and the insect shows tremors, paralysis and dies. It is stable and not easily washed away, so it remains active for a long time. (For the same reason of persistence and accumulation in the food chain, DDT is now banned or restricted in most countries.)
Figure: Chlorobenzene needs drastic conditions
Figure: Benzyl chloride reacts easily
Chlorobenzene reacts with aqueous \(NaOH\) only at about 623 K and 300 atm (Dow’s process), because:
1. The lone pair of chlorine is in resonance with the ring, so the \(C-Cl\) bond has a partial double bond character and is strong and short.
2. The carbon is \(sp^2\) hybridised and holds the bonding electrons of \(C-Cl\) tightly.
3. The ring is electron-rich, so it repels the \(OH^-\) ion, and the phenyl cation is not stabilised, so the \(S_N1\) path is not possible, and \(S_N2\) back-side attack is blocked by the ring. So drastic conditions are needed to force the substitution, and the sodium phenoxide formed gives phenol on acidification: \(C_6H_5Cl+2NaOH\rightarrow C_6H_5ONa+NaCl+H_2O\).
Benzyl chloride (\(C_6H_5CH_2Cl\)) has the chlorine on an \(sp^3\) carbon outside the ring, and the \(C-Cl\) bond is a pure single bond, which is weaker. In the \(S_N1\) path the chloride ion leaves easily to form the benzyl carbocation \(C_6H_5CH_2^+\), which is stabilised by resonance with the benzene ring, so the activation energy is low. The \(S_N2\) path is also easy, because the carbon is not hindered. So it is hydrolysed readily under mild conditions to benzyl alcohol: \(C_6H_5CH_2Cl+NaOH\rightarrow C_6H_5CH_2OH+NaCl\).
Trichloromethane is an aliphatic halide. Its \(C-Cl\) bonds are pure single bonds of a \(sp^3\) carbon, and they are comparatively weak and polar. Zinc and hydrochloric acid give nascent hydrogen, which replaces chlorine by hydrogen (reduction), so chloroform is reduced to dichloromethane:
Chlorobenzene does not react with \(Zn/HCl\). Its \(C-Cl\) bond is strong because of the resonance of the lone pair of chlorine with the ring (partial double bond character) and the \(sp^2\) hybridisation of the ring carbon. So the mild reducing agent cannot break the bond. Chlorobenzene is reduced to benzene only by stronger conditions, for example with \(Ni-Al/NaOH\), \(Na/C_2H_5OH\) or \(Zn\) with strong alkali (nascent hydrogen).
i) Nitrobenzene to Chlorobenzene
Figure: Nitrobenzene to chlorobenzene
ii) Chlorobenzene to Aniline
Figure: Chlorobenzene to aniline
iii) Chlorobenzene to Benzoic acid
Method A (through the nitrile):
Figure: Chlorobenzene to benzoic acid through benzonitrile
Method B (through the Grignard reagent):
Figure: Chlorobenzene to benzoic acid through the Grignard reagent
iv) Chlorobenzene to Phenol
Figure: Chlorobenzene to phenol (Dow’s process)
4. View PDF Notes
i. Handwritten Notes
ii. Typed PDF Notes
5. Frequently Asked Questions
What are haloarenes? (Haloarenes class 12)
What topics are included in Unit 9 Haloarenes of NEB Class 12 Chemistry?
How are haloarenes named?
What are the isomers of C6H4Cl2?
How is chlorobenzene prepared in the laboratory?
What is the difference between the Sandmeyer reaction and the Gattermann reaction?
What are the physical properties of chlorobenzene?
Why does chlorobenzene have a higher boiling point than benzene?
Why are haloarenes less reactive than haloalkanes towards nucleophilic substitution?
Under what conditions does nucleophilic substitution occur in chlorobenzene?
How is chlorobenzene reduced to benzene?
Why is chlorine an ortho-para director but also a deactivating group?
What are the products of nitration, sulphonation, halogenation and Friedel-Crafts reactions of chlorobenzene?
Why does Friedel-Crafts alkylation of chlorobenzene give a poor yield?
What are the Fittig and Wurtz-Fittig reactions?
How is DDT prepared from chlorobenzene?
Why are polychlorinated biphenyls (PCBs) banned?
Why does chlorobenzene not react with aqueous NaOH easily while benzyl chloride does?
What are the uses of haloarenes?
How can chlorobenzene be converted to phenol, aniline and benzoic acid?
Where can I get Class 12 Chemistry Haloarenes notes in PDF (Haloarenes notes PDF)?
Where can I get Class 12 Chemistry notes of NEB (handwritten, PDF, Nepal)?
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