13C linewidths

C Linewidth (Hz), Nuclear Overhauser Enhancement Factor (p), and T- (s), for Linear PS and 1% Cross-Linked PS in Chloroform and Dimethylformamide. 

Bain and co-workers [115] studied the field dependence of 13C linewidths for polyacrylates crosslinked to low levels. The linewidth was directly proportional to field strength, consistent with a significant contribution from a dispersion of chemical shifts arising from new chain structures. In addition the authors used the Delays Alternating with... 

Many components of food are in the solid state and possess very short T2. The linewidths from solid components are generally too wide to be observed directly by solution state NMR methods. However, these components can be detected by the special techniques of solid state NMR. These techniques involve the use of cross polarization excitation (from 3H to 13C), high power 3H decoupling (to inhibit... 

The 13C NMR sensitivity can sometimes be a problem, but for the kind of samples studied here the effective concentration of monomer units is several molar which does not place excessive demands on present Fourier transform NMR spectrometers. In addition to the sensitivity of the chemical shift to structure (9), the relaxation of protonated carbons is dominated by dipole-dipole interaction with the attached proton (9). The dependence of the relaxation parameters T, or spin-lattice, and Tor spin-spin, on isotropic motional correlation time for a C-H unit is shown schematically in Figure 1. The T1 can be determined by standard pulse techniques (9), while the linewidth at half-height is often related to the T2. Another parameter which is related to the correlation time is the nuclear Overhauser enhancement factor, q. The value of this factor for 13C coupled to protons, varies from about 2 at short correlation times to 0.1 at long correlation... 

Adamantane (C10H16) External referencing for 13C spectra, optimizing Hartmann-Hahn match, linewidth measurement, sensitivity measurement [30]... 

In the ENDOR spectrum (Fig. 2b), however, the resolution is greatly improved so that transitions of the two nitrogens, of four carbons (13C enriched), and of a large number of protons with linewidths between 10 and 50 kHz can be detected. 

Solid-state 13C NMR showed significant linewidth broadening of the quaternary aromatic carbon, methine, and methylene carbons in the linear PS. This is consistent with the internal PS chains in the pores of the zeolite being more confined by their environment than in pure PS (without any zeolite). 

Al3+-exchanged synthetic hectorite is a good catalyst for these conversions, and the 13C NMR spectrum obtained in the interlamellar, proton-catalyzed addition of water to 2-methylpropene is indistinguishable (Fig. 79) from that of f-butanol. Doubtless studies of this kind, where natural-abundance, 3C NMR signals are used to probe the chemical identity and motional freedom of reactant and product species situated in the interlamellar spaces of clays or pillared clays (see below), will become increasingly popular. Using l3C NMR linewidths and spin-lattice relaxation studies, Matsumoto et al. (466) have succeeded in discriminating between the internal and external surfaces of pillared montmorillonites. 

Among several indicators of motional state of organic solids H linewidths has been used from very beginning of solid-state NMR. However, inherently low resolution of H MAS NMR spectra caused by the very strong homonuclear interactions and relatively low MAS speed lead to a very limited application of H MAS NMR for studies of mobility.1 A 2D wideline separation (WISE) experiment correlates carbon chemical shifts recorded under MAS with broad H lines.1,24 As a result a broad ll lines are separated in the components corresponding to the 13C sites in their close proximity. For mobile domains in a sample, the H - ll coupling are relatively weak which leads to relatively narrow 11 static lines. The opposite is observed for the rigid domains. 

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