Haloalkanes and Haloarenes
Hydrocarbons are the parent of all organic compounds. When one or more hydrogen atoms of a hydrocarbon are replaced by halogen atoms, the compound becomes a halogen derivative.
Halogen : Bromine, chlorine, fluorine and iodine are the members of halogen family. Halogens are usually represented by the letter X.
Hydrocarbon and Haloalkane
In halogen derivative compounds, the halogen atom acts as a functional group. Halogen derivatives are classified as bromo, chloro, fluoro or iodo according to the type of halogen present.
The halogen derivatives of alkanes are called haloalkanes.
In haloarenes, the halogen atom is directly attached to an aromatic ring.
Halogen containing compounds are very useful in medical cares. For example, chloromycetin (a chlorine containing antibiotic) is used for the treatment of typhoid fever. Halothane (an anaesthetic agent) is used during surgery.
For more theory, please refer to Wikipedia.
Nature of the C-X Bond
The C-X bond (carbon-halogen bond) is polar because halogens are more electronegative than carbon atoms.
The strength of carbon-halogen bond decreases with the size of halogen atom due to increase in bond length and decrease in bond dissociation energy.
Strength of C−X bond → C−F > C−Cl > C−Br > C−I.
Nomenclature of Haloalkanes and Haloarenes.
Question : Which of the following order regarding bond enthalpy ε(C−X) in an alkyl halide (RX) is
Answer : Bond enthalpy C−X (where X is Cl, Br, I) decreases with increase in atomic number of X. Hence, the correct order is : ε(C−Cl) > ε(C−Br) > ε(C−I).