The fi-endpoint energies of 6 neutron-rich nuclei with mass numbers A=146 and A--147 have been measured with a plastic scintillator telescope at the on-line mass separator OSTIS. With the Q,-values derived from these experiments and with those obtained in earlier studies, nuclear structure effects in this part of the nuclear chart are investigated. In addition, nuclear masses derived from the experimental Q~-values are compared with the predictions of theoretical mass calculations.