Recall from Section 9-7 how acetylide ions are alkylated by displacing unhindered alkyl halides.
Like acetylide ions, Grignard and organolithium reagents are strong bases and strong nucleophiles. Fortunately, they do not displace halides as easily as acetylide ions do. If they did displace alkyl halides, it would be impossible to form the reagents from alkyl halides because whenever a molecule of reagent formed, it would react with a molecule of the halide starting material. All that would be formed is a coupling product. In fact, coupling is a side reaction that hurts the yield of many Grignard reactions.
1-bromobutane reacts in the presence of lithium and copper iodide to and this on reacting with 1-bromo butane gives octane
Ethylene bromide reacts in the presence of lithium and copper iodide to give intermediate and this on further reaction gives 3-phenylpropene.