Obtained results indicate that electronwithdrawing substituents increase the bond dissociation enthalpy
(BDE) andionization potential (IP), while electrondonating ones cause a rise in the proton affinity (PA).
Regarding the capacity for transferring electrons, the chemical potential is essential, as well as thermochemical parameters such as bond dissociation enthalpy
(BDE), gap energy, Fukui indices, and charge distribution of HOMO-LUMO orbitals to determine sites of nucleophilic and electrophilic attack.
The antioxidative mechanisms mentioned above are characterized with the thermodynamic parameters: bond dissociation enthalpy
(BDE) related to (1), ionization potential (IP) related to (2a), proton dissociation enthalpy (PDE) related to (2b), proton affinity (PA) related to (3a), and electron transfer enthalpy (ETE) related to (3b).
Bond dissociation enthalpy
(BDE) associated with the bond breaking of labile atoms (e.g., hydrogen in the O-H bond) that lead to formation of radical species is the main parameter related to hydrogen atom transfer (HAT), the most important mechanism of antioxidant activity.