Structure and naming
Halogen derivatives form when one or more hydrocarbon hydrogens are replaced by F, Cl, Br, or I. In a haloalkane R–X, the C–X bond is polar because X attracts electron density: Cδ+–Xδ−. Name the longest carbon chain, number from the end giving the substituent the lowest locant, and use fluoro-, chloro-, bromo-, or iodo-. Examples are chloroethane, 1-bromopropane, and 2-bromopropane.
Properties and bonding
Many haloalkanes are poorly soluble in water because they cannot replace enough water-water attraction, though their C–X bond is polar. Boiling point generally increases with molecular size and polarizability; branching and structure also matter. Properties and toxicity vary greatly, so a class name never replaces substance-specific hazard data.