haloalkane

Take an alkane and swap one of its hydrogens for a halogen — fluorine, chlorine, bromine, or iodine — and you get a haloalkane. Chloroform, the refrigerant in old fridges, the bromoethane on a stockroom shelf: these are haloalkanes. That one halogen completely changes the molecule's personality, turning an inert hydrocarbon into a reactive workhorse.

A haloalkane (also called an alkyl halide) is a compound R-X, where R is an alkyl group and X is a halogen. The key is the carbon-halogen bond. Halogens are more electronegative than carbon, so the bond is polarized: the carbon carries a partial positive charge and the halogen a partial negative charge. This makes the carbon electrophilic — hungry for electron-rich partners — and makes the halogen a potential leaving group that can depart taking the bonding electrons with it. That single polar, breakable bond is why haloalkanes are the textbook substrates for substitution and elimination reactions.

Haloalkanes are central to organic chemistry as reactive building blocks: a nucleophile can displace the halogen to install almost any new group, or a base can pull off a neighbouring hydrogen to make an alkene. They are classified, like the carbon they sit on, as primary, secondary, or tertiary, and that classification strongly influences which reaction pathway dominates. In the wider world some halocarbons are notorious — CFCs once damaged the ozone layer — which is part of why greener alternatives are an active concern.