#halogenoalkane

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Halogenoalkanes

These are created through radical substitution (see the post on that for more). The general formula for halogenoalkanes with one halogen is : "C(n)H(2n+1)X" where X shows a halogen such as Br or Cl There are Primary, Secondary and Tertiary halogenoalkanes, depending on the number of R groups or hydrogen atoms the adjoining carbon is attached to (like alcohols) The C-X bond has a dipole. The X is d-  and the carbon is d+.  This leaves it open to "attack" by negative nucleophiles, such as aqueous OH- ions. X- is a stable ion on its own, so X is substituted easily. This is known as nucleophilic subtitution.  Because the C-F bond is the strongest (highest bond enthalpy), and the C-I bond is the weakest, fluoroalkanes are the least reactive and iodoalkanes are the most reactive. 

image from http://www.chemhume.co.uk

Halogenoalkanes also react with water, in a hydrolysis reaction, to make alcohol.  C2H5Br + H20 ---> C2H5OH + HBr.   

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The radical substitution of an alkane with chlorine

1) Inititation - first, the radicals have to be made. * represents a radical. Cl2 (+UV radiation) ---> 2Cl*    this is homolytic fission   2) Propagation - this is where the radical substitution takes place.  CH4 + Cl* ---> CH3* + HCl CH3* + Cl2 ---> CH3Cl + Cl* Remember for two step propagations like this, or the decomposition of ozone, the catalyst has to come out the other side for the reactions to keep happening. If it doesn't...you've gone wrong :P 3) Termination - this is how the reaction stops: the radicals are "mopped up" Cl* + Cl* ---> Cl2   (ie you turn off UV and it stops breaking down) CH3* + CH3* ----> C2H6  (ethane)  CH3* + Cl* ---> CH3Cl (chloromethane)  As you can see, ethane is produced, as well as some other chemicals like CH2Cl2. This kind of radical substitution is difficult to control.