Using kinetic and mechanistic monitoring by high-performance liquid chromatography and C-13 nuclear magnetic resonance, we have shown that in formaldehyde-free conditions the reactivity of substituted phenols towards condensation reactions arises from several factors. In particular, the groups reacting among themselves may be of two types : either a non-substituted or ortho or para aromatic carbon, or the methylene carbon of a hydroxymethyl group. In addition to the difference in the nature of the group, its position on the aromatic ring is predominant, and the reaction in the para position is favoured. Thus, a third factor participates in the mechanism and kinetics of reaction : the ionization constant of the phenol, which increases with the substitution of phenol and favoured the formation of phenate. We thus show that, in the conditions chosen, two reaction mechanisms participate and the reactivity of sites depends on ring substitution by hydroxymethyl groups.