--%>
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 : Calculation of molecular weight Provide

    Provide solution of this question. In an experiment, 1 g of a non-volatile solute was dissolved in 100 g of acetone (mol. mass = 58) at 298K. The vapour pressure of the solution was found to be 192.5 mm Hg. The molecular weight of the solute is (vapour pressure of ace

    		•
  • Q : Problem based on molarity Select the

    Select the right answer of the question. If 18 gm of glucose (C6H12O6) is present in 1000 gm of an aqueous solution of glucose, it is said to be: (a)1 molal (b)1.1 molal (c)0.5 molal (d)0.1 molal

    		•
  • Q : Calculate molarity of a solution

    Provide solution of this question. Molarity of a solution prepared by dissolving 75.5 g of pure KOH in 540 ml solution is: (a) 3.05 M (b) 1.35 M (c) 2.50 M (d) 4.50 M

    		•
  • Q : Henry law question Answer the following

    Answer the following qustion. The definition “The mass of a gas dissolved in a particular mass of a solvent at any temperature is proportional to the pressure of gas over the solvent” is: (i) Dalton’s Law of Parti

    		•
  • Q : Problem on reversible process a. For a

    a. For a reversible process involving ideal gases in a closed system, Illustrate thatΔS = Cv ln(T2/T1) for a constant volume process ΔS = Cp ln(T2/T1) for a constant pressu

    		•
  • Q : DNA Organic Explain DNA organic in

    Explain DNA organic in brief?

    		•
  • Q : Linde liquefaction process Liquefied

    Liquefied natural gas (LNG) is produced using a Linde liquefaction process from pure methane gas at 3 bar and 280 K (conditions at point 1 in figure below). A three-stage compressor with interceding is used to compress the methane to 100 bar (point 2). The first stage

    		•
  • Q : Relative lowering of the vapour pressure

    Choose the right answer from following.The relative lowering of the vapour pressure is equal to the ratio between the number of: (a) Solute moleules and solvent molecules (b) Solute molecules and the total molecules in the solution (c) Solvent molecules and the tota

    		•
  • Q : Problem on melting of ice A) It has

    A) It has been suggested that the surface melting of ice plays a role in enabling speed skaters to achieve peak performance. Carry out the following calculation to test this hypothesis. Suppose that the width of the skate in contact with the ice has been reduced by sh

    		•
  • Q : Strength of any solution Give me answer

    Give me answer of this question. A solution contains 1.2046 x 1024 hydrochloric acid molecules in one dm3 of the solution. The strength of the solution is: (a) 6 N (b) 2 N (c) 4 N (d) 8 N

    		•