Halogenation of alkanes
Alkanes react with Cl2 or Br2 in the presence of ultraviolet light (The ultraviolet region of the electromagnetic spectrum is between wavelengths 10–6 and 10–4 cm. The ultraviolet region is adjacent to the visible region.). In this reaction
For alkanes with more than three carbons, there is more than one type of hydrogen and mixtures of organic products are formed as shown below for propane.
the hydrocarbon skeleton stays intact and
if the hydrocarbon is present in large excess only one C-H bond in the reactant alkane is replaced by a C-X (X = Cl, Br) bond in the product.
CH3CH2–H + Cl–Cl
CH3CH2–Cl + H–Cl
if the hydrocarbon is present in large excess only one C-H bond in the reactant alkane is replaced by a C-X (X = Cl, Br) bond in the product.
CH3CH2–H + Cl–Cl
CH3CH2–Cl + H–Cl This type of reaction where two reactants exchange parts is referred to as a substitution.
In the example above the green H and the green Cl swap places.
For alkanes with more than three carbons, there is more than one type of hydrogen and mixtures of organic products are formed as shown below for propane.
CH3CH2CH3 
CH3CH2CH2Cl + 
CH3CH2CH2Cl + It is common in organic reactions to focus on the organic reactants and products.
These are presented as above in an equation format where the equation is definitely NOT balanced.
These are presented as above in an equation format where the equation is definitely NOT balanced.
Thus the reagent is shown above the arrow as above.
Inorganic products are not shown (HCl is also formed in the reaction of propane with Cl2 above.)
When different organic products are formed from the same reaction (as above) the + between them actually means "and".
This "equation" is an organic chemist's shorthand for saying propane reacts with chlorine in the presence of light to form both 1-chloropropane and 2-chloropropane.
Inorganic products are not shown (HCl is also formed in the reaction of propane with Cl2 above.)
When different organic products are formed from the same reaction (as above) the + between them actually means "and".
This "equation" is an organic chemist's shorthand for saying propane reacts with chlorine in the presence of light to form both 1-chloropropane and 2-chloropropane.