Structural Determination in Carbonaceous Solids Using Advanced Solid State NMR Techniques

Abstract

Detailed structural information in carbonaceous solids with complex molecular structures may be obtained with a combination of three advanced solid-state NMR techniques, i.e., dipolar dephasing with variable dephasing times, 13C CP/MAS spectral editing, and an isotropic−anisotropic correlation experiment called PHORMAT. It is shown that the ratio of protonated to nonprotonated aromatic carbons may be determined with high accuracy by the conventional dipolar dephasing experiment with variable dephasing times. The fractions of aliphatic CH, CH2, CH3 and nonprotonated (C) carbons may be obtained by employing 13C CP/MAS spectral editing techniques. The 2D PHORMAT experiment is used to obtain the structural information in the aromatic region of coal. Theoretical predictions of the principal values of chemical shift tensors in model compounds are used in the interpretation of the experimental chemical shift tensors. The potential application of these methods is illustrated using a sub-bituminous coal DIETZ (PSOC-1488).