Based on density functional theory (DFT), to investigate relationships between the antioxidant activity
and structure of dihydrocaffeic acid, quantum chemical calculation is used. The optimized structures
of the neutral, radical and ionic forms have been carried out by DFT-B3LYP method with the
6-311G(d,p) basis set. Reaction enthalpies related with the hydrogen atom transfer (HAT), single
electron transfer proton transfer (SET-PT) and sequential proton loss and electron transfer (SPLET)
were calculated in gas and water phase. The HOMO-LUMO energy gap, electron affinity,
electronegativity, ionization energy, hardness, chemical potential, global softness and global
electrophilicity were calculated by using the same level of theory. Surfaces with a molecular electrostatic
potential (MEP) were studied to determine the reactive sites of dihydrocaffeic acid. The difference in
energy between the donor and acceptor as well as the stabilization energy was determined through the
natural bond orbital (NBO) analysis. The Fukui index (FI) based on electron density was employed to
predict reaction sites. Reaction enthalpies are compared with previously published data for phenol
and 3,4-dihydroxycinnamic acid.