Results are presented from a quantum mechanical/molecular mechanical coupled potential simulation of the ionic fragmentation of tert-butyl chloride in water. The calculated barrier to fragmentation is found to be in good accord with experimental estimates. This result is only obtained if long-range electrostatic interactions are taken into account via a Born correction or a reaction field. Unfortunately, while these methods improve the quality of the energetic results, they do not do so uniformly. Analysis of solute and solvent structure along the reaction path is also discussed.