--%>
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 : M ive me answer of this question. When

    ive me answer of this question. When mercuric iodide is added to the aqueous solution of potassium iodide, the: (a) Freezing point is raised (b) Freezing point is lowered (c) Freezing point does not change (d) Boiling point does not change

    		•
  • Q : Describe Enzyme Catalyzed reactions

    Many enzyme catalyzed reactions obeys a complex rate equation that can be written as the total quantity of enzyme and the whole amount of substrate in the reaction system. Many rate equations that are more complex than first and se

    		•
  • Q : Equimolar solutions Select the right

    Select the right answer of the question. Equimolar solutions in the same solvent have : (a)Same boiling point but different freezing point (b) Same freezing point but different boiling poin (c)Same boiling and same freezing points (d) Different boiling and differe

    		•
  • Q : Molecular Symmetry Types The number of

    The number of molecular orbitals and molecular motions of each symmetry type can be deduced. Let us continue to use the C2v point group and the H2O molecule to illustrate how the procedure develop

    		•
  • Q : Problem on molarity-normality-molality

    Can someone please help me in getting through this problem. The solution ofAl2(SO4)3 d = 1.253gm/m comprise 22% salt by weight. The molarity, normality and molality of the solution is: (1) 0.805 M, 4.83 N, 0.825 M (2)

    		•
  • Q : Product of HCl Zn Illustrate  the

    Illustrate  the product of HCl Zn?

    		•
  • Q : Determining of normality of sodium

    Can someone please help me in getting through this problem. The normality of a solution of sodium hydroxide 100 ml of which includes 4 grams of NaOH is: (a) 0.1 (b) 40 (c) 1.0 (d) 0.4

    		•
  • Q : Simulate the column in HYSYS The

    The objective of this work is to separate a binary mixture and to cool down the bottom product for storage. (Check table below to see which mixture you are asked to study). 100 kmol of feed containing 10 mol percent of the lighter component enters a continuous distillation column at the m

    		•
  • Q : P block bif3 is ionic while other

    bif3 is ionic while other trihalides are covalent in nature

    		•
  • Q : Haloalkene with the help of polarity of

    with the help of polarity of c-x bond show that aryl halides are less reactive than alkyl halides

    		•