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This article outlines our current understanding of the structure of coal in terms of both the chemical and physical bonding processes responsible for its structural integrity and the extensive network of pores that permeate the organic material. Information on the microscopic chemistry of coal and its relationship to coal's physical structure and reactivity is an essential component in the successful development ofthe next generation ofcoal conversion technologies. Although coal is an extremely complex and heterogeneous material, many of its fundamental properties can be determined by the coordinated efforts oforganic and physical chemists, solid state physicists, and chemical engineers. The scientific questions that emerge from these efforts lie at the frontiers of chemistry and physics research.Coal and coal products will play an increasingly important role in fulfilling the energy needs ofour society. Future applications will extend far beyond the present major uses for power generation, metals processing, and chemicals production. A key feature in these extensions will be the development of means to convert coal from its native form into useful gases and liquids in ways that are energy efficient, nonpolluting, and economical. The design of this next generation of conversion processes will require a deeper understanding ofcoal's intrinsic properties and the ways in which it is chemically transformed under process conditions. Coal properties-such as the chemical form of the organic material, the types and distribution of organics, the nature of the pore structure, and the mechanical propertiesmust be determined for coals of different ranks (or degrees of coalification) in order to use each coal type most effectively (1).A second and more subtle challenge is to identify the chemical pathways followed during the thermal conversion ofcoal to liquids or gases. This is accomplished by tracing the conversion of specific chemical functional groups in the coal and studying the effects of various inorganic compounds on the conversion process. Significant progress has been made in this area by combining test reactions with a battery of characterization techniques. The ultimate goal is to relate the structure of the native coal to the resulting conversion products.A briefdescription ofcoal from three different points ofview illustrates the dimensions of the problem. Structurally, coal is a complex system (Fig. 1). Organic material dominates, typically representing 85-95% (wt/wt) of a dry coal. These organic materials occur in various different petrographic types, called "macerals," which reflect the nature of the precursor plant material. Various inorganic materials, particularly aluminosilicates and pyrites (especially in high-sulfur coals), comprise 5-15% of the coal. A third structural element, and perhaps its most distinctive feature when compared to other solid fossil fuel sources like petroleum and oil shale, is an extensive network of pores. These pores give coal a high surface area (> 100 m2/g for bitumi...