Induction of the Phase 2 enzymes is a major strategy in the chemoprotection against cancer. Inducers belong to nine different chemical classes. In this contribution we found that a measure of the tendency of thirty plant phenylpropenoids and synthetic analogues to release electrons correlates linearly with their potency in inducing the activity of NAD(P)H:quinone reductase (NQO1), a prototypic Phase 2 cancer protective enzyme.  The tendency to release electrons was determined by the energy of the highest occupied molecular orbital (EHOMO), calculated by simple quantum mechanical methods. The correlations observed establish a clear conclusion: the smaller the absolute Energy of the Highest Occupied Molecular Orbital (EHOMO) of an agent, the greater its inducer potency, (i.e., the lower its oxidation potential, the stronger its electron donor property and the greater its inducer potency). The finding of this redox ranking of the inducers demonstrates that it is possible to predictively control the genetic expression of an enzymatic defense against cancer by xenobiotics via one physical parameter, their EHOMO.