  Assuming a binary reaction mechanism, the yield of isotopes near the heaviest
$N=Z$ neutron-deficit nucleus $^{100}$Sn is studied with a microscopic
transport model. The large influence of nuclear shell structure and isotope
composition of the colliding nuclei on the production of exotic nuclei is
demonstrated. It is shown that the reaction $^{54}$Fe+$^{106}$Cd seems to be
most favourable for producing primary exotic Sn isotopes which may survive if
the excitation energy in the entrance reaction channel is less than about 100
MeV. In the case of large differences in the charge (mass) numbers between
entrance and exit channels the light fragment yield is essentially fed from the
decay of excited primary heavier fragments. The existence of optimal energies
for the production of some oxygen isotopes in the binary mechanism is
demonstrated for the $^{32}$S+$^{197}$Au reaction.
