Chemical association introduces essential modifications in the microscopic structure of disordered materials, as new species are formed and the density of reactants deceases. These radical changes in the microscopic structure cannot be adequately captured by the pair distribution function, and hence descriptions of the electronic structure at the level of the effective medium approximation break down. We here propose a novel approach closely connected with the single superchain/effective medium approximation, in which the effects of chemical association are explicitly built-in. The new approximation has been tested in a simple minded model of alkali metal, namely a hard sphere fluid with a one-level tight-binding Hamiltonian with transfer matrix elements modeled by Yukawa terms. This fluid is thought to undergo a dimerization process to yield hard dumbbells via an intermediate stage in which a mixture is present. The proposed approach reproduces the band structure obtained by direct diagonalization for various stages along the reaction path, while retaining the simplicity of a linear theory.