Cross polarization and magic angle sample spinning NMR spectra of model organic compounds. 2. Molecules of low or remote protonation

Abstract

Cross polarization/magic angle sample spinning (CP/MAS) 13C NMR spectra were obtained at various contact times on five solid organic compounds containing carbon atoms far from intramolecular protons or containing very few hydrogen atoms. Carbon atoms four or more bonds from the nearest intramolecular proton cannot be fully polarized before ,,( ) effects begin to dominate the proton magnetization. Rapid molecular motion aggravates the problem because of motional attenuation of the dipolar interaction. Computer-fitted TCii and Tlp(H) parameters are consistent with these experimental results. The simple theories of cross polarization account for incomplete polarization in these cases. In l,2:4,5-benzenetetracarboxylic dianhydride, C10H2O6, the relative aromatic and carbonyl signal intensities are only 5% from the ideal values on the basis of atomic ratios, but absolute intensities can be seriously reduced. In general, CP/MAS NMR provides a convenient and useful quantitative method for studying diamagnetic, organic solids of low molecular weight that is competitive to other physical methods even for molecules of low or remote protonation.

Influence of production variables and starting material on charcoal stable isotopic and molecular characteristics

“…For example, carbon atoms remote from protons, (e.g. quaternary carbons) may be underrepresented, due to slower rates of cross polarization (Alemany et al, 1983). We have therefore elected to compare only the relative intensity of components in the broader groupings of aliphatic (alkyl and O-alkyl), and aromatic structures.…”

How to measure absolute P3HT crystallinity via 13C CPMAS NMR

“…[19] As a result, CP kinetics depends on local proton density and organic functionality, as was shown in previous works. [20,21] CP transfer is complicated further in highly motionally averaged 1 H spin systems, such as the hexyl side-chain protons of P3HT, so one must be careful to ensure that relative peak intensities in the spectrum are proportional to the mole fraction of 13 C, and hence meaningful. In order to explore the impact of CP conditions on the 13 C NMR intensity, CPMAS spectra were taken as a function of MAS rate, temperature, CP time, and Hartmann-Hahn matching field strength (B 1 ).…”

Airborne Contamination of Forest Soils by Carbonaceous Particles from Industrial Coal Processing

“…In CP experiments, the polarization energy for carbon nuelei is transferred via hydrogen nuelei with an efficiency depending on the proximity of these nuelei. Consequently, the carbon nuelei in condensed structures are underestimated by CP experiments (Alemany et al, 1983;Snape et al, 1989). To detect such carbons we performed Bloch decay experiments, in which carbon nuelei were polarized directly.…”