Part III. FUNCTIONAL CLASSES OF ORGANIC COMPOUNDS

Chapter 10 HALOHYDROCARBONS

10.1. Classification and nomenclature

Halohydrocarbons (or organic halides) are hydrocarbon derivatives in which one or more halogen atoms replace the hydrogen atom(s).

Depending on the halogen nature, fluoro, chloro, bromo, and iodo derivatives are known, as well as derivatives containing various halogen atoms simultaneously.

For halohydrocarbons, radicofunctional nomenclature is often used, which is sometimes simpler than the substitutitive one. In the examples below, along with names by the substitutive nomenclature, radicofunctional names are given in parentheses.

The isomerism of halohydrocarbons is determined by the isomerism of the carbon skeleton and the halogen atom position. Haloalkanes are classified as primary, secondary, or tertiary ones, depending on the carbon atom to which the halogen is attached.

Halohydrocarbons are also subdivided according to the hybridization type of the carbon atom to which the halogen is bound. So, in haloalkanes, the halogen atom is bonded to the sp³-hybridized carbon. In haloarenes (ArHal) and haloalkenes of the vinylic type (RCH=CHHal), the halogen is bonded to the sp²-hybridized carbon. Halides of the allylic type (RCH=CHCH₂Hal) and benzylic type (ArCH₂Hal) are also well known.

10.2. Physical properties

The physical properties of halohydrocarbons depend on the nature and number of halogen atoms in the molecule (Table 10.1). Lower and middle haloalkanes are colorless gases or liquids with a peculiar sweet odor. The boiling points of haloalkanes

with the same hydrocarbon group rises in the series of fluoro, chloro, bromo and iodosubstituted ones. Higher homologs and some polyhalogenated derivatives are colorless crystalline substances. Polyfluoroalkanes differ markedly in properties from other halides (see Section 10.4).