When a haloalkance is heated at 573 K or at a slightly lower temperature in the presence of anhydrous aluminium chloride as catalyst, the halide undergoes rearrangement to form isomeric haloalkane. So this reaction is an isomerism reaction.
1-Chloropropane CH3CH2CH2Cl rearranges to 2-Chloropropane. Chlorine is attached to the 2nd carbon (or middle carbon) instead of the 1st carbon or terminal carbon
If there is no hydrogen atom on the carbon adjacent to the C-X group, rearrangment occurs and methyl group migrates providing the opportunity for the halogen atom to occupy the position.
1-Chloro-2,2 dimethyl propane rearranges to 2-Chloro-2-methylbutane