Evaluation of the chemical reactivity in lignin precursors using the Fukui function

The hydroxycinnamyl alcohols: p-coumarol, coniferol and sinapol are considered the basic units and precursors of lignins models. In this work, the specific reactivity of these molecules was studied. We investigate their intrinsic chemical reactivity in terms of the Fukui function, applying the principle of hard and soft acids and bases (HSAB) in the framework of the density functional theory (DFT). Comparisons of their nucleophilic, electrophilic and free radical reactivity show their most probably sites to form linkages among them. It is found that the most reactive sites, for reactions involving free radicals, are the carbons at the β-position in the p-coumarol and sinapol molecules, whilst the regions around the carbon-oxygen bond of the phenoxyl group are the most reactive in coniferol. Figure Isocontour plots for the free radical form of the Fukui function f ⁰ (r), showing the reactive sites toward electron-rich/poor reactants