Halogenated compounds

Halogenated compounds (also called halogenated combinations and haloalkanes or alkyl halides, for those derived from alkanes) are a class of organic compounds that formally derive from hydrocarbons, by replacing hydrogen atoms with halogen atoms, respectively: fluorine, chlorine, bromine or iodine.

Compounds are also widespread in nature; for example, bromomethane is a component of ocean waters.

Structural isomerism

The number of structurally isomeric compounds that can arise in this way is very large. Only from methane derives 4 halogenated compounds, which are CH3Cl, CH2Cl2, CHCl3 and CCl4. From ethane, another example, 9 chlorinated derivatives are possible and known: CH3CH2Cl, CH3CHCl2, CH3CCl3, CH2ClCCl3, CHCl2CCl3, CCl3CCl3, CH2ClCH2Cl, CH2ClCHCl2, CHCl2CHCl2.

Physical properties

Halogenated compounds are colorless substances (except polyiodides). The first terms in the homologous series of haloalkanes are gaseous at ordinary temperature, the others are liquids. The lower terms of the series have low melting points, the higher ones and the disubstituted aromatic derivatives (in the even position), as well as the polysubstituted ones, are solids.

The density of brominated and iodinated compounds is generally higher than that of water, of monochlorinated ones somewhat lower. The density of iodinated compounds is higher than that of the corresponding brominated compounds, and the density of brominated compounds higher than that of chlorinated compounds (ρ(CH3I)=2.29; ρ(CH3Br)=1.73; ρ(CH3Cl)=0.953)

Halogenated compounds are practically insoluble in water; in organic solvents, such as hydrocarbons, alcohols, ether, it dissolves easily. Aliphatic halogenated compounds have sweet smell and narcotic properties. In high concentration they are toxic. Benzyl chloride, but especially bromide and iodide, are strongly lachrymatory.