In their theoretical investigation, Meir et al. modeled two Diels-Alder reactions with and without electric fields of varying sign and magnitude . The first reaction was the cycloaddition of ethylene and cis-butadiene to form cyclohexene (see Scheme 1) where they found that an electric field oriented along the "reaction axis" pointing from the butadiene to the ethylene (the negative z direction; electric field direction points positive to negative) lowered the reaction barrier, but a field in the opposite direction did not raise the reaction barrier. Using this conventionally "simple" example of the charge density response to an electric field, we will examine the inter-atomic and intra-atomic redistribution of electron charge density that underly the response of 𝜌 through the reaction and from the applied fields.