Electropositive metals such as sodium, potassium, magnesium, zinc, etc. can insert into alkyl halides, breaking the carbon-halide bond 
( halide could be chlorine, bromine, iodine ) and forming a carbon-metal bond. This reaction happens via a SET mechanism ( single-electron-transfer mechanism ). If magnesium reacts with an alkyl halide, it forms a Grignard reagent, or if lithium reacts, an organolithium reagent is formed. Thus, this type of insertion reactions has important applications in chemical synthesis.