Molecular composition and mobility of torbanite precursors: Implications for the structure of coal

Coorongite, a torbanite precursor found in South Australia, and algal residues derived from Botryococcus braunii and other algae have been examined by solid-state ¹³C NMR techniques. The majority of carbon in these materials is present as (CH₂)_n. However, variable-temperature studies show that a considerable proportion of the alkyl chains have unusual dipolar-dephasing behavior and are more mobile than in rigid solids. It is suggested that these mobile structures contribute to the so-called "guest phases" in coal. The data are also consistent with a vascular and algal model of coal.