Nomenclature

Common names put the alkyl group first and then the halide (methyl chloride). IUPAC names treat the compound as a hydrocarbon carrying a halo substituent (chloromethane).

For monohalobenzenes the common and IUPAC names coincide. Dihalobenzenes take o-, m-, p- in common names but the locants 1,2-, 1,3- and 1,4- in IUPAC names.

Dihalides with both halogens on one carbon are geminal (gem-dihalides, common name alkylidene halides); with the halogens on neighbouring carbons they are vicinal (vic-dihalides, alkylene dihalides). IUPAC calls both dihaloalkanes.

Name pairs to know: sec-butyl chloride = 2-chlorobutane; neo-pentyl bromide = 1-bromo-2,2-dimethylpropane; tert-butyl bromide = 2-bromo-2-methylpropane; vinyl chloride = chloroethene; allyl bromide = 3-bromopropene.

More pairs: methylene chloride = dichloromethane; chloroform = trichloromethane; bromoform = tribromomethane; carbon tetrachloride = tetrachloromethane; n-propyl fluoride = 1-fluoropropane; benzyl chloride = chlorophenylmethane; o-chlorotoluene = 1-chloro-2-methylbenzene (or 2-chlorotoluene).

C₅H₁₁Br has eight structural isomers. Primary: 1-bromopentane, 1-bromo-3-methylbutane, 1-bromo-2-methylbutane, 1-bromo-2,2-dimethylpropane. Secondary: 2-bromopentane, 3-bromopentane, 2-bromo-3-methylbutane. Tertiary: 2-bromo-2-methylbutane.