alkylhalogenidi

Alkyl halides, also known as haloalkanes, are organic compounds in which one or more halogen atoms (fluorine, chlorine, bromine, or iodine) replace a hydrogen atom on an sp3-hybridized carbon of an alkyl group. The general formula is R–X, where R denotes an alkyl group and X the halogen. They can be mono-, di-, or polyhalogenated, and are commonly classified by the degree of substitution of the carbon bearing the halogen (primary, secondary, tertiary). Alkyl halides differ from vinyl and aryl halides, in which the halogen is bonded to an sp2 carbon.

The carbon–halogen bond strength and the leaving-group ability of the halide influence reactivity. Iodine and bromine are better leaving groups than chlorine, which is better than fluorine. Consequently, SN2 substitutions occur readily for primary (and methyl) halides in polar aprotic solvents, while SN1 reactions are favored for tertiary halides. Elimination reactions (E1 and E2) compete under basic conditions or elevated temperatures, producing alkenes. Typical reactions include nucleophilic substitutions with hydroxide, cyanide, or alkoxide; formation of Grignard reagents (RMgX) from alkyl halides; and reductions to alkanes under appropriate conditions. Alkyl halides can be prepared by converting alcohols with reagents such as thionyl chloride (SOCl2), phosphorus tribromide (PBr3), or phosphorus trichloride (PCl3/PCl5), or by hydrohalogenation of alkenes.

Applications and properties: Alkyl halides are versatile intermediates in organic synthesis, used to form alcohols, ethers, amines, and other functional groups, and they serve as precursors in pharmaceutical and agricultural chemicals. They span a wide range of physical properties, generally increasing in boiling point with molecular weight and halide size. Many are volatile and potentially toxic; handling requires appropriate safety measures. Some halogenated species raise environmental concerns, including ozone-depletion or persistence, underscoring the need for responsible use and disposal.