Dihalidien

Dihalidien, often referred to as dihalides, are chemical compounds that contain two halogen atoms, typically fluorine, chlorine, bromine, or iodine, in their structure. They are commonly categorized by how the halogen substituents are arranged on the carbon framework: 1,1-dihalides (geminal dihalides), where both halogens sit on the same carbon, and 1,2-dihalides (vicinal dihalides), where the halogens are on adjacent carbons. Examples of geminal dihalides include dichloromethane (CH2Cl2) and dibromomethane (CH2Br2). Examples of vicinal dihalides include 1,2-dichloroethane (Cl-CH2-CH2-Cl) and 1,2-dibromoethane (Br-CH2-CH2-Br). Inorganic dihalides form MX2 compounds such as iron(II) chloride (FeCl2) and zinc chloride (ZnCl2).

Dihalides display a range of properties depending on whether they are organic or inorganic. Organic dihalides often exist as liquids or volatile compounds and are commonly used as intermediates in organic synthesis. Inorganic dihalides, as metal halide precursors, are typically crystalline solids and are important in catalysis, materials science, and chemical vapor deposition.

Preparation and typical reactions vary with type. Organic dihalides are usually prepared by halogenation of hydrocarbons: addition of halogen to alkenes yields vicinal dihalides, while stepwise halogenation or specific synthetic routes can give geminal dihalides. Dihalides can undergo elimination reactions to form alkenes or alkynes, especially vicinal dihalides under strong base or metal-amide conditions (twofold dehydrohalogenation). They also serve as versatile intermediates for cross-coupling, cyclization, and the construction of more complex molecules.

See also: geminal dihalides, vicinal dihalides, metal dihalides.