The polychlorinated compounds captafol (CPL) and 2,6-dichloroisonicotinic acid (INA) are able to protect plants acting as a fungicide or an inductor of plant resistance, respectively. At the same time, CPL and INA are dangerous for the respiratory organisms, i.e. mammalians, bacteria, and fungi. The high electron-withdrawing ability of these compounds enables them to serve as unnatural electron acceptors in the cellular ambient near to electron transport pathways located in the thylakoid membrane of chloroplasts or in the mitochondrial respiratory chain. Low-energy electron attachment to CPL and INA in vacuo leads to formation of many fragment species mainly at thermal electron energy as it is shown using dissociative electron attachment spectroscopy. On the basis of the experimental findings, assigned with the support of density functional theory calculations it is suggested that the different bioactivity of CPL and INA in respiratory and photosynthetic organisms is due to the interplay between the dissociative electron attachment process and the energies of electrons leaked from the electron transport pathways.