N-Bromosuccinimide reacts with aromatic aldehydes in the solid state to yield exclusively nuclear brominated products while a similar reaction in the solution phase produces a number of products under varied conditions. The reactivity and regioselectivity have been studied in terms of the energies of HOMO, HOMO–LUMO difference, reaction free energy, reaction conditions and crystal packing. Single crystal X-ray structural analysis of 3, 4- ...