The November 12, 1966, solar eclipse has been modeled by a large multispecies chemistry code and the results compared with the numerous experimental measurements that were made at that time. Measured preeclipse values of electron density and code-predicted values agree closely by ionization by precipitating electrons from the radiation belts is included. Current gas-phase ion chemistry does not predict the rapid decrease and subsequent reconstitution of electron about totality in the 65- to 85-km region, nor does it produce the large number of negative ions above 70 km that can be inferred from the experimental data. While basic constraints can be placed on the electron attachment processes because of the experimental data, an entirely new class of physical processes may need to be included to explain this phase of D region behavior.