Organic Synthesis

The halide of the alkyl halide attacks the AlCl3. The delta positive side of the alkyl group is attacked by the double bond electrons of the aromatic, bonding the alkyl carbon to the aromatic ring, and leaving a carbocation at the other side of the now missing double bond. The extra hydrogen (beside the alkyl group) can be removed by a base, leaving it's electrons to reform a double bond (and the aromaticity) or the electrons can shift to the other side of the added group and do the same thing.