In this tutorial, I will present a few specific applications in which the need for an explicit treatment of the electronic structure of the solute is particularly important and cannot be conveniently circumvented by developing a problem-specific force field. The examples include the computation of the pKa of organic acid in the electronically excited state, the solvatochormic shifts of an organic chromophore from steam vapor to ambient water, the vibrational energy relaxation of a ligand in the enzyme active site, and the kinetic isotope effects in a proton transfer reaction in water using Feynman path integrals.