[en] The single particle (hole) energies in ¹⁰⁰Sn, as extrapolated by a shell model analysis of the neighbouring nuclei, show a remarkable similarity to those in ³⁶Ni, one major shell lower. This is borne out in nearly identical I^π=2⁺ excitation energies, implying E(2⁺)≅3 MeV in ¹⁰⁰Sn, and a large neutron effective E2 charge ε≥1.6ε. In contrast a small proton polarisation charge δε≤0.3ε is found, pointing to a large isovector charge. Mean field predictions for single particle energies show substantial deviations from the experimental extrapolation. From the experimental two-proton hole spectrum in ⁹⁸Cd an improved empirical interaction is extracted for the π(p_1/2,g_9/2) model space yielding a good description of the N=50 isotones ⁹⁵Rh to ⁹⁸Cd. In ¹⁰⁴Sn, for the first time in this region, strong E3 transitions with B(E3)≥17 W.u. were identified, indicating E(3^-)≅3 MeV in ¹⁰⁰Sn. New experimental devices, as the Ge-cluster cube and total absorption spectrometers, applied in a pioneering experiment to the β⁺/EC decay of ⁹⁷Ag, have led to a consistent picture of the Gamow-Teller quenching around ¹⁰⁰Sn. The experimental results are discussed in the framework of various shell model approaches by using both empirical and realistic interactions. (orig.)