Classification of Alkyl Halide

The elements falling in group 17 of the periodic table are halogens such as F, Cl, Br, I. A halide forms when a chemical compound involves halogens as one of its atoms. Halides are essential in human life, and they occur naturally as acids or salts and are found in minerals, plants, and animals. The most common halide salt used in our everyday lives is sodium chloride (NaCl). The Alkyl halides or haloalkanes are carbon compounds having a halogen as a functional group. The classification of alkyl halide includes primary, secondary, and tertiary alkyl halides. 

What are Alkyl Halides?

Alkyl halides are compounds formed when a hydrogen atom in a hydrocarbon is replaced by a halogen (F, Cl, Br, I) in any of the bond positions depending upon the classification of alkyl halide. The bonds present in the hydrocarbon can be single, double, or triple. A general formula to describe alkyl halides can be defined as CnH2n+1X, where X is the halogen. The terminology to define an alkyl halide is quite simple, wherein we write the name of the alkyl group, followed by the name of the halogen present ending with -ide. For example, a hydrocarbon chain containing three carbons and fluorine as a functional group will be named propyl fluoride if the fluorine group is attached to carbon-1. Another acceptable name is 1-Fluoropropane. 

Classification of Alkyl Halide

The classification of alkyl halide important to understand how these are formed. There are three categories into which alkyl halides can be majorly classified. These are

1. Primary alkyl halide – These occur when the carbon-containing halogen atom is connected to just one alkyl group on its side. For example, 1-Bromoethane and 1- Chloropropane. However, it does not matter how much of a complicated carbon chain is present in the compound. 
2. Secondary alkyl halide – This type of alkyl occurs when the carbon-containing halogen atom is connected to two alkyl groups on its sides. For example, 2-Bromobutane and 2-chloropropane. Here, it is evident that the halogen is connected to the second carbon atom in the carbon chain.  
3. Tertiary alkyl halide – This type of alkyl occurs when the carbon-containing halogen atom is connected to three alkyl groups on its sides. For example, tertiary-butyl-iodide is a tertiary alkyl halide. Here, the halogen atom is connected to carbon surrounded by alkyl groups on three sides. 

Physical Properties

1. These hydrocarbons hold many important physical properties, such as being odourless and colourless. 
2. Alkyl halides are known to be hydrophobic. 
3. Alkyl halides possess higher melting and boiling points when compared with alkanes having the same number of carbon atoms. Since the halogen atom adds electronegativity in the hydrocarbon, the dipoles present get polarised due to the London dispersion phenomenon. Due to this polarisation, the intermolecular forces increase in the compounds giving rise to the unique properties of the alkyl halides. 
4. The properties of alkyl halides also get modified according to the classification of alkyl halide. Some of the alkyl halides are also used in fire extinguishers as they are inflammable compared to their analogous alkanes. 
5. The solubility of such compounds is high due to the polarisation present, and they are slightly soluble in water. As the mass of the halogen increases down the group,, the density of RI>RBr>RCl>RF implies that alkyl iodides are heavier than other alkyl halides. 

Alkyl Halide Uses

The uses are strongly based on the classification of alkyl halide. The various uses of alkyl halides range from industrial to pharmaceutical applications and are described below. 

1. Alkyl Halides are majorly used as solvents for compounds that are non-polar. 
2. Polyvinyl Chloride (PVC), Polytetrafluorethylene (Teflon), or chlorofluorocarbons (CFCs) are popularly known as alkyl halides in industrial applications such as in refrigerators, air-conditioners, propellants, fire extinguishers, etc. 
3. Chlorine is a halogen that has antibiotic properties and is thus useful for curing typhoid fever. 
4. The alkyl halides containing fluorine group are used as a substitute for blood in many surgeries and thus hold tremendous potential in pharmaceuticals. 
5. Alkyl halides containing fluorine and chlorine are used to prepare Teflon coating, which is useful for utensils, automobiles, etc. 

Conclusion

Alkyl halides are carbon compounds containing one or more halogen atoms and are classified based on primary, secondary, and tertiary compounds. They hold a variety of uses and applications due to their unique set of properties such as high melting and boiling point, polarisation, hydrophobic in nature, colourlessness, and odourlessness.