Many times in the Lab, we lose money and time in vain, because we do not know whether reactions are more productive and faster in the gas phase or in aqueous solutions. By determining the barrier heights of the reactions via Computational Chemistry, it is easy to have faster and more productive reactions which can occur either in the gas phase or in aqueous solution. In this book, the energy barriers for SN2 ligand exchange reactions between the chloride anion and para-substituted benzyl chlorides were investigated both in water solution and in the gas phase by using quantum chemical...