--%>
Assignment Help - homework help

What are the chemical properties of haloalkanes?

Haloalkanes are extremely reactive category of aliphatic compounds. Their reactivity is due to the presence of polar carbon-halogen bond in their molecules.


The chemical reactions of haloalkanes can be divided into four ways:
    
Nucleophilic substitution reactions

In haloalkanes, the halogen atoms are attached to the carbon atom. The bond between carbon and halogen is polar in character because the halogen atom is more electronegative than carbon.

Due to the presence of partial positive charge on the carbon atom, the nucleophilies can attack on electron deficient carbon thereby resulting the displacement of weaker nucleophile is generally stronger than it.

The order of reactivity of various alkyl halides towards nucleophilic substitution in the order:

Order of reactivity: RI > RBr > RCI > RF

This order of reactivity can be explained on the basis of strength of C-X bond. The C-X bond is the weakest in R-I and the strongest in R-F as is clear from the bond energy data for methyl halides. In fact, the C-F bond is so strong that organic fluorides do not undergo nucleophilic substitution under ordinary conditions.

Bond

C-I

C-Br

C-Cl

C-F

Bond Enthalpies (kJ/mole)

234

293

351

452

Bond length (pm)

214

193

178

139

Dipole moment (Debye)

1.636

1.830

1.860

1.847


Examples of nucleophilic substitution reactions of haloalkanes
    
Replacement of hydroxyl group (Formation of alcohols).

Haloalkanes on treatment with aqueous solution of KOH or moist silver oxide (Ag2O/H2O) give alcohols.
                        
2388_haloalkanes.png 
    
Replacement Alkoxy group (Formation of ethers). (Williamson Synthesis):

Haloalkanes on treatment with alcoholic sodium or potassium alkoxide form ethers. This reaction is called as Williamson Synthesis.
        
1935_haloalkanes1.png 

Ethers can also be prepared by heating alkyl halides with dry silver oxide, Ag2O
                
1005_haloalkanes3.png  
    
Replacement by Cyano Group (Formation of cyanides or nitrites)

Haloalkanes on treatment with alcoholic KCN solution give alkanenitriles or alkyl cyanides as the major product with a small amount of alkyl isocyanide.

2173_haloalkanes2.png 

The reaction of alkyl halides with KCN gives us an important method for increasing the length of carbon chain by one carbon atom i.e. rising of series.

   Related Questions in Chemistry

  • Q : Water under pressure problem-henry law

    Can someone help me in going through this problem. The statement “When 0.003 moles of a gas are dissolved in 900 gm of water under a pressure of 1 atm, 0.006 moles will be dissolved under the pressure of 2 atm", signfies: (a)

    		•
  • Q : Distribution law Help me to go through

    Help me to go through this problem. The distribution law is applied for the distribution of basic acid between : (a) Water and ethyl alcohol (b) Water and amyl alcohol (c) Water and sulphuric acid (d) Water and liquor ammonia

    		•
  • Q : Biodegradable polymers what are the

    what are the examples of biodegradable polymers

    		•
  • Q : Problem on mole fraction of glucose

    Provide solution of this question. While 1.80gm glucose dissolve in 90 of H2O , the mole fraction of glucose is: (a) 0.00399 (b) 0.00199 (c) 0.0199 (d) 0.998

    		•
  • Q : Entropy on molecular basis. The

    The equation S = k in W relates entropy to W, a measure of the number of different molecular level arrangements of the system.In the preceding developments it was unnecessary to attempt to reach any "explana

    		•
  • Q : Colligative effect Choose the right

    Choose the right answer from following. Which one of the statements written below concerning properties of solutions, explain a colligative effect: (a) Boiling point of pure water decreases by the addition of ethano (b) Vapour pressure of pure water d

    		•
  • Q : Explain the polymers and its types.

    Polymers are the chief products of modern chemical industry which form the backbone of present society. Daily life without the discovery and varied applications of polymers would not have been easier and colourful. The materials made of polymers find multifarious uses and applications in all walk

    		•
  • Q : Amines arrange in decreasing order of

    arrange in decreasing order of basicity pi pyridine,pyridine,pyrrole, morphine

    		•
  • Q : Importance of organic chemistry

    Describe the importance of organic chemistry?

    		•
  • Q : Describe Point Groups. For any

    For any symmetric object there is a set of symmetry operations that, together, constitute a mathematical group, called a point group.It is clear from the examples that most molecules have several elements of symmetry. The H2O

    		•