Halides

Halide is usually defined as a binary compound of a halogen with a more electropositive element or radical. Some halides have a covalent bond, some may have an ionic bonds, halide minerals of a group are naturally occurring inorganic compounds that are salts of halogen acids, a metal that usually occurs as a halide is a silver. These metal halides are used in high-intensity discharge lamps, Silver halides are used in photographic films and papers. The silver halides that have been exposed to light are reduced to metallic silver when the film is developed, generating an image; halides are also used in the solder paste. A halide ion is a halogen atom bearing a negative charge.

The halide anions are fluoride (F−), chloride (Cl−), bromide (Br−), iodide (I−), and astatide (At−). Such ions are present in all ionic halide salts. Halide minerals contain halides. 

Some of the examples of halides are: Copper (II) Chloride (CuCl2), Silver chloride (AgCl), Calcium chloride (CaCl2), Iodoform (CHI3), Sodium Chloride (NaCl)

The general formula for halides is, MX (X = F, Cl, Br, or I)

Alkyl halides

Alkyl halides are compounds in which one or more hydrogen atoms in an alkane are replaced by halogen atoms (fluorine, chlorine, bromine, or iodine). Therefore, the general formula for alkyl halides that contains one halogen atom is (CNH2N+1X), alkyl halides are also called haloalkanes. Alkyl halides are the derivatives of alkanes that can be obtained by replacing one hydrogen atom with a halogen atom. Alkyl halides are the mono halogen derivatives of alkanes that are generally referred to as alkyl halides. 

The name of the parent hydrocarbon is used to give alkyl halides their common names. Alkyl halides can easily be prepared from alcohols upon the addition of halides. The hydroxyl group of alcohol is replaced by a halogen atom linked to the other chemical in this process. Primary alkyl halide (1◦ alkyl halide; primary haloalkane; 1◦ haloalkane): An alkyl halide (haloalkane) in which the halogen atom (F, Cl, Br, or I) is bonded to a primary carbon. X = any atom other than carbon (usually hydrogen).

Among the methods used in industry, and occasionally in the laboratory, to produce simple alkyl halides is direct halogenation of alkanes. When an alkane such as methane is treated with Cl2 or Br2 in the presence of heat or light, a mixture of alkyl halides is formed by successive chlorination reactions. Although alkyl halides are polar, they are incapable of forming hydrogen bonds with water molecules. Hence they are sparingly soluble in water. However, organic solvents such as alcohols, ethers, and benzene make them soluble.

Aryl Halides

Aryl halide is a molecule having a halogen atom attached to an sp2 hybridized carbon in an aromatic ring directly. Aryl halides have the generic formula ArX, where Ar is phenyl, substituted phenyl, or aryl groups. Aryl halides can be prepared by mixing the solution diazonium salt from the primary aromatic amine with cuprous chloride or cuprous bromide. In a Sandmeyer’s reaction, a diazonium salt is reacted with copper (I) bromide, copper (I) chloride, or potassium iodide (KI) to form the respective aryl halide. Although aryl halides do not undergo nucleophilic substitution reactions by SN1 and SN2 mechanisms those having one or more nitro groups at ortho or para to the halogen undergo nucleophilic substitution reactions under mild conditions.

Allylic Halide

Allylic halides are compounds containing halogen atoms bonded to sp3 hybridized C-atom next to carbon double bond. 3-Chloro cyclohexane-1-ene. This is an example of an allylic halide, these and benzyl halides give SN1 and SN2 reactions. Allyl halides also give an SN2 mechanism.

Conclusion

Alkyl halides are being used in our day-to-day lives more widely. Small haloalkanes are among the most often used solvents in chemical laboratories; chlorofluorocarbons are widely utilised as refrigerants and propellants, and compounds containing both Br and F are widely used as refrigerants and propellants are often used in fire retardants Alkyl halides can react with Sn2 or Sn1 mechanisms. Sn2 requires a good nucleophile (like I-) and a polar aprotic solvent (like acetone). Primary and Secondary halides react well with Sn2 reactions but not with tertiary because of the steric hindrance.