Alkanes are compounds of carbon and hydrogen. Alkanes have the general formula as C_nH_(2n+2). Halogen family comprises five elements namely fluorine, chlorine, iodine, bromine, and astatine. Haloalkanes are derived from saturated hydrocarbons when one or more hydrogen atom is replaced by a halogen atom. Although haloalkanes are derived from alkanes, there is a large difference between their structural and physical properties. If alkanes and haloalkanes containing the same number of carbons are compared, it can be observed that the boiling point of alkanes are lower than those of haloalkanes. Alkanes are non-aromatic while some of the alkyl halides have an associated smell. Since alkyl halides are compounds formed from alkanes and halogen, they are named after their parent constituents. Consider ethane reacting with chlorine. The resultant haloalkane is called chloroethane. However, this is for a single chlorine molecule. If the number of chlorine molecules is four, then the resultant will be called tetrachloroethane wherein tetra depicts four molecules of chlorine. Also Known As: Haloalkanes, halogenoalkanes, halogenated hydrocarbons General Formula: R-X Where R represents hydrocarbon (alkane) and X represents halogen. As mentioned earlier, the general formula of an alkane is C_nH_(2n+2). One or more hydrogen is replaced by a halogen atom. Types of Alkyl Halides Alkyl halides can be classified depending on the atom of carbon to which the halogen atom is bonded. Primary (1^o): The carbon atom bonded to the halogen atom is bonded to one other alkyl group. Secondary (2^o): The carbon atom bonded to the halogen atom is bonded to two other alkyl groups. Tertiary (3^o): The carbon atom bonded to the halogen atom is bonded to three other alkyl groups. Two examples of alkyl halides are presented below. Example I Consider the chlorination of methane (CH₄) as represented in the image below. When two atoms of chlorine are added to methane, a bond between central carbon atom and hydrogen is broken whereas central carbon and a chlorine bond is formed. The freed hydrogen atom combines with a chlorine atom to form hydrochloric acid. The resultants are chloromethane and hydrochloric acid (HCL) whose structures have been presented. Chloromethane is toxic, colorless, pleasantly smelling, and highly flammable. It is used as weed killer, as a solvent in chemical reactions, anesthetic in medicine field, manufacture of silicon polymers, and petroleum refining process. Example II Consider the chlorination of chloromethane (CH₃Cl) as represented in the image below. When two atoms of chlorine are added to chloromethane, a bond between central carbon atom and hydrogen is broken whereas central carbon and a chlorine bond is formed. The freed hydrogen atom combines with a chlorine atom to form hydrochloric acid. The resultants of this reaction are dichloromethane and hydrochloric acid (HCL) whose structures have been presented. Dichloromethane is a volatile, colorless, pleasantly smelling liquid which is insoluble with water. It is used as a degreaser, solvent for chemical processes, aerosol propellant, and heat engine (in drinking bird). In the end, process of distillation is used to separate these products. Note that both the above reactions can take place only in presence of UV light or high temperatures. Alkyl halides find wide applications in the field of chemistry. However, the fact that these compounds have serious implications on health and environment cannot be ignored. Carbon tetrachloride used as a fabric cleaner is known to cause damage to liver. Similarly, chloroform a popular anesthetic has been proven to be cancerous. Therefore, use and circulation of alkyl halides has been restricted to some extent.