What are Alkyl Halides? 

A functional group is a collection of several atoms or bonds with certain characteristic chemical properties and reactions associated with it. There is a presence of a halogen atom (F, Cl, Br, or I; it represents any halogen atom), as a functional group in alkyl halides. Therefore, it can be said that alkanes that contain a halogen compound are called alkyl halides. 

Alkyl halides fall into different classes that depend on how the halogen atom is positioned on the chain of carbon atoms; these classes of compounds have different chemical differences in reaction and structure. 

Nomenclature for Alkyl Halides 

Many organic compounds are related to the hydrocarbon class of alkanes and this similarity is incorporated into the common names of compounds.  

The systematic way of naming alkyl halides is to name the halogen as a substituent, like an alkyl group, and then use numbers to indicate the position of the halogen atom present on the main chain. The name of the halogen as a substituent comes from the stem of the element’s name plus the ending with -o, so the substituent names of the halogens are  fluoro-, chloro-, Bromo- and iodo-. 

The reactions of alkanes with halogens produce halogenated hydrocarbons, that is, compounds in which one or more hydrogen atoms of a hydrocarbon have been replaced by halogen atoms. The replacement of a single hydrogen atom gives an alkyl halide (haloalkane). The common chemical names of alkyl halides fall under two parts: the name of the alkyl group and the stem of the name of the halogen that goes with the ending or suffix, -ide. 

In IUPAC nomenclature, there are substitutive and functional class systems for naming organic halogen compounds.  The substitutive system is preferably used over the functional classification system for naming organic halogen compounds according to IUPAC rules. In the substitutive method of IUPAC nomenclature, the alkyl halides are named "haloalkanes". A root word is chosen based on the number of carbon atoms present in the parent chain and the primary suffix "-ane" is added.  Finally, "halo" is prefixed to it.  

The infix "cyclo" is added immediately before the root word for halogen compounds containing cyclic moieties. 

Alkyl halides are derived from alkanes by exchanging hydrogen for halogen (fluorine, chlorine, bromine, and iodine). The dependence on the degree of substitution at the carbon atom carrying the halogen is inevitable. Some examples of the naming alkyl halides are given below. 

IUPAC name for alkyl halides 

Types of Alkyl Halides

Alkyl halides fall into different classes that depend on the position of the halogen atom within the chain of carbon atoms. Alkyl halide structures can be classified as primary, secondary, and tertiary. The chemical reactivity of several alkyl halides is based on their structures and functions associated with them. Since the neutral bonding pattern for halogens is one bond and three lone pairs, the carbon and halogen always share a single bond. 

Alkyl Halide Reactions 

The functional group of alkyl halides is a carbon-halogen bond, the most common halogens being fluorine, chlorine, bromine, and iodine. Except for iodine, these halogens have electronegativities significantly greater than a carbon atom. Therefore, this functional group is polarized so that the carbon atom is electrophilic and the halogen atom is nucleophilic. The two characteristics other than electronegativity also influence the chemical behavior of these compounds. The first being covalent bond strength and the second, the relative stability of the corresponding halide anions 

One reaction which is found to be common to alcohols as well as to alkyl halides is the elimination reaction. It involves the removal of the functional group (either X or OH) and an H atom from an adjacent carbon. The removal of both the functional group as well as the H atom results in the formation of a double bond between the carbons. Thus, it can be said that the saturated alkane becomes unsaturated after undergoing elimination reactions. 

Besides the similarity, the biggest difference between elimination in alkyl halides and in alcohols is the identity of the catalyst: for alkyl halides, the catalyst is a strong base and for alcohols, the catalyst is a strong acid. Due to this difference, several reactions along with different reagents have been employed. 

Applications of Alkyl Halides 

These classes of compounds find wide applications in industry as well as in our daily life. They are used as solvents for relatively non-polar compounds and starting materials for the synthesis of organic compounds. The chlorine-containing antibiotic is chloramphenicol which is produced by soil microorganisms is very effective for the treatment of typhoid fever.  

Synthetic halogen compounds, viz. chloroquine are used for the treatment of malaria; halothane is used as an anesthetic during surgery. In surgery, some fully fluorinated compounds are being considered as potential blood substitutes. Organic compounds containing halogen are relatively rare in terrestrial plants and animals.  

Common Mistakes 

• Students might fail to identify the difference between alkanes, alkenes, and alkynes. 
• Students might fail to identify the functional group. 
• Identifying and naming a branched and cyclic alkyl halide is to be done correctly. 
• The different properties of an alkyl halide due to which difference in various reactions shown by them also needs focus. 

Context and Application

This topic is useful for various undergraduate and postgraduate courses, especially for Bachelors and Masters in Chemistry and various science courses at the high school level. 

Related Concepts 

• Functional group
• IUPAC 
• Hydrocarbon 
• Types of elimination reactions
• Aliphatic
• Aromatic