  A relativistic finite nucleus calculation using a Dirac optical potential is
used to investigate the importance of final state interactions [FSI] at large
momentum transfers in inclusive quasielastic electronuclear reactions. The
optical potential is derived from first-order multiple scattering theory and
then is used to calculate the FSI in a nonspectral Green's function doorway
approach. At intermediate momentum transfers excellent predictions of the
quasielastic $^{56}$Fe$(e,e')$ experimental data for the longitudinal response
function are obtained. In comparisons with recent measurements at $|{\vec
q|}=1.14$~GeV/c the theoretical calculations of $R_L$ give good agreement for
the quasielastic peak shape and amplitude, but place the position of the peak
at an energy transfer of about $40$~MeV higher than the data.
