Halogenalkane

Halogenalkane, or haloalkane, is an organic compound in which one or more hydrogen atoms of an alkane have been replaced by a halogen atom (fluorine, chlorine, bromine, or iodine). The general formula is R–X, where R is typically an alkyl group and X is a halogen. When more than one halogen is present, or if the halogen is attached to a carbon that also bears other substituents, the compound is still categorized as an alkyl halide. Haloalkanes are commonly named by substitutive nomenclature, for example chloromethane, bromoethane, or 1-iodopropane; common names such as methyl chloride are historical.

Halogenalkanes are usually polar compounds due to the C–X bond, with boiling points that generally increase with molecular weight and halogen size. They range from gases and volatile liquids at room temperature, depending on the size of the R group and the halogen.

Reactivity is dominated by the carbon–halogen bond. Alkyl halides undergo nucleophilic substitution (SN1 or SN2) and elimination (E1 or E2) under suitable conditions. SN2 is favored by primary halides and good nucleophiles, and proceeds with inversion at the reactive carbon. SN1 predominates for tertiary halides in polar solvents. The leaving group ability typically follows I > Br > Cl > F. Halogenalkanes are also used to prepare Grignard reagents RMgX in dry ether solvents.

Applications include serving as solvents (e.g., dichloromethane, chloroform), reagents in organic synthesis, and intermediates for pharmaceuticals, agrochemicals, and polymers. Some haloalkanes are volatile and toxic, with environmental concerns and regulatory controls. Proper handling and disposal are important, and many haloalkanes are subject to restrictions due to toxicity or environmental impact.