Polyene model of coal structure and metamorphism

Eight coal ranks (G, GZhO, GZh, K, KO, KS, and T) are investigated by IR spectroscopy in the range between 1800 and 650 cm–1, with polynomial decomposition of the spectra obtained. The similarities and differences in the IR spectra for two series of coal are noted: specifically, fat coal (Zh, GZh, GZhO, and G) and coking coal (K, KO, KS, and T). For both series, we consider the regions of the spectra containing narrow absorption bands. On passing from Zh and G coal in the fat set and from K to T coal in the coking set, the intensity of the IR absorption bands at 1450 and 1370 cm^–1 declines, on account of deformation C?H vibrations of the CH₂ and CH₃ groups, while the absorption of oxygen-bearing groups appears. These experimental data are inconsistent with accepted concepts regarding the metamorphism on passing from gas coal (rank G) to lean coal (rank T).