The poly-cyclic units of Pittsburgh No. 8 coal (PIT), on the average, lie in short-range structural domains of ca. three layers. The species C14H9 is consistent with the average PCA unit in PIT, and its radius is similar to2.9 Angstrom. The average distance between the PCA layers in the short-range domains of PIT is similar to3.9 Angstrom. The addition of pyridine molecules to PIT does not alter structuring within the PCA units to an extent measured by wide-angle X-ray scattering experiments, and it appears that the interlayer structuring within the short-range structural domains in PIT is also not altered to a measurable extent. Rather, the quasi-stable adduct is formed between the three-layer domains of PIT and the pyridine molecules.