Monohalogenated

Monohalogenated is an adjective used in chemistry to describe compounds in which exactly one halogen atom is substituted into an organic molecule. The term applies to fluorine, chlorine, bromine, iodine, or astatine, and distinguishes such species from dihalogenated or polyhalogenated compounds that contain two or more halogen atoms.

Common examples include chloromethane (CH3Cl), fluorobenzene (C6H5F), and monochloroethane (C2H5Cl). In systematic naming, the halogen is indicated by substituent prefixes such as fluoro-, chloro-, bromo-, or iodo- attached to the parent hydrocarbon.

Preparation and occurrence: Monohalogenation is typically achieved by halogenation reactions that replace a single hydrogen with a halogen, such as radical halogenation of alkanes, electrophilic aromatic substitution on benzene to yield chlorobenzene or bromobenzene, and halogenation of alkenes followed by rearrangements. These reactions produce monohalogenated products with varying reactivity depending on the halogen and the substrate.

Properties and uses: The carbon–halogen bond is a reactive handle for further transformations, making monohalogenated compounds useful intermediates in organic synthesis, pharmaceuticals, dyes, and polymers. Physical properties depend strongly on the halogen type and the molecular framework; for instance, chloromethane is a gas at room temperature, while chlorobenzene is a liquid.

Safety and environmental considerations: Some monohalogenated compounds are toxic, volatile, or environmentally persistent. Proper handling, containment, and regulatory compliance are important for their manufacture and use.