It is shown that shock waves whose structure is determined solely by the effects of chemical reactions (reaction-resisted shock fronts) are possible and completely analogous to relaxation - resisted waves. A single dissociation reaction is considered and numerical results indicate that such waves could be observed experimentally. Bulk viscosities equivalent to reaction effects are possibly 10[to the power of 2] or more times shear viscosity values. (Examples are based on Lighthill's ideal dissociating gas).