Publication costs assisted by Ames Laboratory ESR, pulse NMR, and multiple pulse NMR were used to study free radical concentrations, and the extent to which protons in coals may be characterized by damping constants under specific radio-frequency pulse sequences in two Virginia vitrains, three Iowa vitrains, and selected model compounds. ESR measurements confirmed previously found correlations between free radical content and carbon content. Electron g factors varying from 2.0025 to 2.0028 are not inconsistent with assignment of free radicals to aromatic ring systems. NMR pulse techniques were used to determine damping constants associated with proton spin-spin and spin-lattice relaxation.Multiple pulse line narrowing experiments were capable of narrowing the proton line width from roughly 30 kHz in all coals to roughly 700 Hz. Comparison of results on coals with pulse and multiple pulse measurements on the model compounds naphthalene, 2-methylnaphthalene, 4,4'-bismethylbenzophenone, m-tolylacetic acid, polystyrene, polyethylene, and polybutadiene indicated the following: (a) roughly 400 Hz of the residual proton line width in the coals under multiple pulse line narrowing experiments is due to free radical electron spin-nuclear spin dipolar coupling, (b) there is not a simple relation between spin-spin damping constants in coals, and aliphatic/aromatic proton ratios, and (c) resolution into aromatic and aliphatic protons will require removal of interproton dipolar interactions, proton chemical shift anisotropies, and electron-proton interactions by a combination of multiple pulse line narrowing experiments and magic angle rotation. The second moments of the proton absorption spectrum decrease with increasing proton concentration. This result is shown not to be an effect of free radical concentration, but is thought to be associated with increasing rigidity of coal structures with age.

The first combined multiple pulse-magic angle experiment is reported in which both homonuclear dipole interactions and chemical shift anisotropies are removed to resolve chemically shifted fluorines. The sample selected was KEL-F.(AIP)

An NMR probe is described which is capable of use in combined multiple pulse–magic angle spinning experiments for removal of homonuclear dipolar broadening and chemical shift anisotropies in randomly oriented samples. Two examples are included to illustrate the utility of the technique.

Combined multiple pulse NMR and sample spinning techniques have been used to obtain the carboxylic acid 1H chemical shift tensor in 2,6-dimethylbenzoic acid. The values obtained were σ⊥=−18.5 ppm and σ∥=−4.2 ppm relative to TMS. A discussion of the changes in line shape of chemical shift tensors under sample rotation is given. This leads to a quantitative expression for the sample rotation speed, ωr≫σzz−1/3Trσ, to define ’’rapid’’ sample rotation.