Concept - Haloalkanes & Haloarenes Class 12 Notes | EduRev

Class 12 : Concept - Haloalkanes & Haloarenes Class 12 Notes | EduRev

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Class XII: Chemistry 
Chapter 10: Haloalkanes and Haloarenes 
Top Concepts  
1. Nature of C-X bond in alkyl halides: X is more electronegative than 
carbon. So, the C-X bond is polarized with C having a partial positive 
charge and X having a partial negative charge 
2. Preparation of haloalkanes: 
 
 
3. Preparation of haloarenes: 
a. By elecrophilic substitution reaction: 
      
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Class XII: Chemistry 
Chapter 10: Haloalkanes and Haloarenes 
Top Concepts  
1. Nature of C-X bond in alkyl halides: X is more electronegative than 
carbon. So, the C-X bond is polarized with C having a partial positive 
charge and X having a partial negative charge 
2. Preparation of haloalkanes: 
 
 
3. Preparation of haloarenes: 
a. By elecrophilic substitution reaction: 
      
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 2
     
b. Sandmeyer’s reaction: 
  
c. Gattermann reaction: 
  
d.  
  
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Class XII: Chemistry 
Chapter 10: Haloalkanes and Haloarenes 
Top Concepts  
1. Nature of C-X bond in alkyl halides: X is more electronegative than 
carbon. So, the C-X bond is polarized with C having a partial positive 
charge and X having a partial negative charge 
2. Preparation of haloalkanes: 
 
 
3. Preparation of haloarenes: 
a. By elecrophilic substitution reaction: 
      
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b. Sandmeyer’s reaction: 
  
c. Gattermann reaction: 
  
d.  
  
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e.  Balz – Schiemann reaction: 
  
4. Physical properties of haloalkanes: 
a. Solubility. Although haloalkanes are polar in nature, yet they are 
practically very slightly soluble in water. In order for a haloalkane to 
dissolve in water, energy is required to overcome the attractions 
between the haloalkane molecules and break the hydrogen bonds 
between water molecules. However Haloalkanes are not able to form 
hydrogen bonds with water and therefore, less energy is released 
when new attractions are set up between the haloalkane and the water 
molecules because these are not as strong as the original hydrogen 
bonds in water molecules. As a result, solubility of haloalkanes in 
water is low. 
b. Density:   
• Simple fluoro and chloroalkanes are lighter than water while 
bromides and polychloro devrivatives are heavier than water. 
• With the increase in number of carbon atoms, the densities go on 
increasing.  
• With the increase in number of halogen atoms, the densities go on 
increasing. 
• The densities increase in the order: 
• Fluoride < chloride < bromide < iodide 
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Class XII: Chemistry 
Chapter 10: Haloalkanes and Haloarenes 
Top Concepts  
1. Nature of C-X bond in alkyl halides: X is more electronegative than 
carbon. So, the C-X bond is polarized with C having a partial positive 
charge and X having a partial negative charge 
2. Preparation of haloalkanes: 
 
 
3. Preparation of haloarenes: 
a. By elecrophilic substitution reaction: 
      
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 2
     
b. Sandmeyer’s reaction: 
  
c. Gattermann reaction: 
  
d.  
  
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e.  Balz – Schiemann reaction: 
  
4. Physical properties of haloalkanes: 
a. Solubility. Although haloalkanes are polar in nature, yet they are 
practically very slightly soluble in water. In order for a haloalkane to 
dissolve in water, energy is required to overcome the attractions 
between the haloalkane molecules and break the hydrogen bonds 
between water molecules. However Haloalkanes are not able to form 
hydrogen bonds with water and therefore, less energy is released 
when new attractions are set up between the haloalkane and the water 
molecules because these are not as strong as the original hydrogen 
bonds in water molecules. As a result, solubility of haloalkanes in 
water is low. 
b. Density:   
• Simple fluoro and chloroalkanes are lighter than water while 
bromides and polychloro devrivatives are heavier than water. 
• With the increase in number of carbon atoms, the densities go on 
increasing.  
• With the increase in number of halogen atoms, the densities go on 
increasing. 
• The densities increase in the order: 
• Fluoride < chloride < bromide < iodide 
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• The density also increases with increasing number and atomic mass 
of the halogen. 
c. Method and Boiling points:  
• Molecules of organic halogen compounds are generally polar. Due 
to the polarity as well as higher molecular mass as compared to the 
parent hydrocarbon, the intermolecular forces of attraction (dipole 
– dipole and van der Waals) between the molecules are stronger in 
halogen derivatives of alkanes. As a result melting and boiling 
points of chlorides, bromides and iodides are considerably higher 
than those of the parent hydrocarbon of comparable molecular 
mass. 
• Amongst themselves, the following trends are observed: 
o For the same alkyl group the boiling points of alkyl chlorides, 
bromides and iodides follow the order RI > RBr > RCl > RF where R 
is an alkyl group. This is because with the increase in the size of 
the halogen, the magnitude of van der Waals force increase. 
o In general, the boiling points of chloro, bromo and iodo compounds 
increase with increase in the number of halogen atoms. 
o For the same halogen atom, the boiling points of haloalkanes 
increase with increase in the size of alkyl groups. 
o For isomeric alkyl halides, the boiling points decrease with 
branching. This is because branching of the chain makes the 
molecule more compact and, therefore, decrease the surface area. 
Due to decrease in surface area, the magnitude of van der Waals 
forces of attraction decreases and consequently, the boiling points 
of the branched chain compound is less than those of the straight 
chain compounds. 
  
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Class XII: Chemistry 
Chapter 10: Haloalkanes and Haloarenes 
Top Concepts  
1. Nature of C-X bond in alkyl halides: X is more electronegative than 
carbon. So, the C-X bond is polarized with C having a partial positive 
charge and X having a partial negative charge 
2. Preparation of haloalkanes: 
 
 
3. Preparation of haloarenes: 
a. By elecrophilic substitution reaction: 
      
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b. Sandmeyer’s reaction: 
  
c. Gattermann reaction: 
  
d.  
  
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e.  Balz – Schiemann reaction: 
  
4. Physical properties of haloalkanes: 
a. Solubility. Although haloalkanes are polar in nature, yet they are 
practically very slightly soluble in water. In order for a haloalkane to 
dissolve in water, energy is required to overcome the attractions 
between the haloalkane molecules and break the hydrogen bonds 
between water molecules. However Haloalkanes are not able to form 
hydrogen bonds with water and therefore, less energy is released 
when new attractions are set up between the haloalkane and the water 
molecules because these are not as strong as the original hydrogen 
bonds in water molecules. As a result, solubility of haloalkanes in 
water is low. 
b. Density:   
• Simple fluoro and chloroalkanes are lighter than water while 
bromides and polychloro devrivatives are heavier than water. 
• With the increase in number of carbon atoms, the densities go on 
increasing.  
• With the increase in number of halogen atoms, the densities go on 
increasing. 
• The densities increase in the order: 
• Fluoride < chloride < bromide < iodide 
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• The density also increases with increasing number and atomic mass 
of the halogen. 
c. Method and Boiling points:  
• Molecules of organic halogen compounds are generally polar. Due 
to the polarity as well as higher molecular mass as compared to the 
parent hydrocarbon, the intermolecular forces of attraction (dipole 
– dipole and van der Waals) between the molecules are stronger in 
halogen derivatives of alkanes. As a result melting and boiling 
points of chlorides, bromides and iodides are considerably higher 
than those of the parent hydrocarbon of comparable molecular 
mass. 
• Amongst themselves, the following trends are observed: 
o For the same alkyl group the boiling points of alkyl chlorides, 
bromides and iodides follow the order RI > RBr > RCl > RF where R 
is an alkyl group. This is because with the increase in the size of 
the halogen, the magnitude of van der Waals force increase. 
o In general, the boiling points of chloro, bromo and iodo compounds 
increase with increase in the number of halogen atoms. 
o For the same halogen atom, the boiling points of haloalkanes 
increase with increase in the size of alkyl groups. 
o For isomeric alkyl halides, the boiling points decrease with 
branching. This is because branching of the chain makes the 
molecule more compact and, therefore, decrease the surface area. 
Due to decrease in surface area, the magnitude of van der Waals 
forces of attraction decreases and consequently, the boiling points 
of the branched chain compound is less than those of the straight 
chain compounds. 
  
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5.  Physical Properties of Haloarenes: 
a. These are generally colourless liquids or crystalline solids. 
b. These are heavier than water. 
c. Melting and boiling points of haloarenes:  
• Melting and boiling points of haloarenes are nearly the same as 
those of alkyl halides containing the same number of carbon atoms.  
• The boiling points of monohalogen derivatives of benzene are in the 
order: iodo > bromo > chloro > fluoro 
• For the same halogen atom, the melting and boiling points increase 
as the size of the aryl group increases. 
• The melting point of para isomer is quite higher than that of ortho 
or meta isomers. This is due to the fast that is has symmetrical 
structure and there fore, its molecules can easily pack loosely in 
the crystal lattice. As a result intermolecular forces of attraction are 
stronger and therefore, greater energy is required to break its 
lattice and it melts at higher temperature.                        
6. Chemical properties of haloalkanes: 
d. Nucleophilic substitution reaction: 
  
Mechanism: 
 
S
N
I  S
N
II   
Rate =k [RX] 
 
Rate =k [RX] [Nu] 
Two step reaction One step reaction 
Inversion of configuration Racemic mixture 
Second order reaction First order reaction 
  
Order : 
CH
3
X < 1
o
 < 2
o
 < 3
o 
Order : 
CH
3
X > 1
o
 > 2
o
 > 3
o 
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