The structure of the major product formed in the following reaction is:

DMF is a polar aprotic solvent, favoring ${\text{S}}_{\text{N}}2$ reactions. However, this is an aromatic nucleophilic substitution (${\text{S}}_{\text{N}}\text{Ar}$).Iodide is a much better leaving group than Chloride. Therefore, the Cyanide nucleophile will replace the Iodine atom.Product: 1-chloro-4-cyanobenzene.