Analytical expressions for the derivatives of the free energy of solution of molecular solutes with respect to the dielectric constant and to a parameter defining the size of the cavity are here presented. These derivatives refer to a version of the model that describes solutes at ab initio Hartree-Fock level (as well as at the classical level) placed within a cavity reproducing the molecular-shape. Attention is paid to the appropriate description of the boundary conditions which determine the integral value of the apparent charge spread on the cavity surface.