Proton NMR of solids

For our purposes, A designates the anisotropic chemical shift (CS), dipolar (D) interactions. The chemical shift implicitly contains the anisotropic molecular susceptibility which places a natural limit on the resolution of proton NMR of solids under conditions of high resolution as discussed by VanderHart [12]. 

Cross Polarization Intensity as a Function of Contact Time. Two-component decays are often seen in the proton NMR of solid block polymers (20,21,22), and have been associated with the presence of two phases with different mobilities. Shafer, et. al. (23) have pointed out that the decay of the cross polarization signal as a function of contact time (which reflects the proton Tjp) can be used to characterize the polymer homogeneity. In the absence of phase separation the proton T]p values for each carbon should be the same. 

Using proton NMR of solutions, the composition of polymers can be analyzed.47 Carbon-13 NMR spectroscopy is a useful tool for studying the sequence length of segments in copolymers and thereby determining the blockiness of the copolymer. With solid-state NMR, the mobility of chain segments can be studied and the crystallinity determined. 

NMR of solids usually give broad featureless absorptions due to the dipolar interactions which, at least in the case of protons, are orders of magnitude larger than the characteristic chemical shifts and spin-spin couplings used for structure elucidation... 

Lippmaa et al. (86) have successfully studied solid state Si NMR of several trimethylsilyl silicate samples using proton-enhanced nuclear induction spectroscopy and magic angle spinning. They showed that the high resolution Si NMR of solids can be useful for structural studies of certain soluble and insoluble silicates, because many of these compounds with well defined molecular structures in the solid state tend to undergo very complicated rearrangements and condensation in solution. (93)... 

It would be of great utility if a better methodology could be provided to monitor polymer-bound reactions than gel phase heteronuclear NMR. However, as previously mentioned, the utility of gel phase proton NMR in solid phase synthesis monitoring is of little value, as the spectra obtained are generally quite broad. 

Section 4 is entirely devoted to ferroelectric and H-bonded systems. It also provides a nice illustration of results that always maintained the utility of proton NMR in solid state, even wideline, or how the old question of the order disorder or displacive nature of some ferroelectric phase transitions were reopened by progresses in NMR resolution. A number of structural phase transition is discontinuous, but the examples of coexistence in solid-state and kinetic studies are rather scarce this is the object of Section 5. Section 6 is devoted to single-crystal studies that allow very precise comprehension of subtle phase transition mechanisms. Section 7 introduces the salient features of NQR that represent an interesting alternative to NMR in some cases. The section ends with a table of miscellaneous phase transitions that complete the references given in the text. Section 8 concludes and presents some perspectives in NMR phase transition studies. 

One of the more recent applications of proton NMR in solid polymers has been the use of multiple quantum coherence (MQCOH), which is developed among clusters of dipolar coupled protons vide infra) to infer details of chain dynamics [20], and (which is another way of making the same statement) local dipolar couplings [21]. 

Fig. 7. Nmr spectra of quinine [103-95-0] C2QH24N2O2, acquired on a Bruker 300AMX spectrometer using a Bmker broadband CP/MAS probe, (a) Proton-decoupled spectmm of quinine in CDCl (b) the corresponding spectmm of solid quinine under CP/MAS conditions using high power dipolar decoupling (c) soHd-state spectmm using only MAS and dipolar decoupling, but without cross-polarization and (d) soHd quinine mn using the...

Badger and coworkers devised a sequential synthesis of [ 18]annulene-l,4 7,10 l 3,16-trioxide which is formally the condensation product of three furan molecules and three ethylenes . The synthesis is illustrated below in Eq. (3.25). The [18]annulene trioxide was obtained as a red solid (mp 215—216 °d) whose proton nmr spectrum showed two peaks of equal area at 8.66 and 8.68 ppm. 

High-Resolution Solid-State NMR Study of Reversible 1,5-Proton Shifts in Organic Solids [90MRC(S)29] NMR of Pyrazoles ... 

Some reviews relevant for this section concern N CPMAS [86AG(E)383] of pyrazoles, including CPMAS results (93MRC107) and proton transfer in solid heterocycles (94JHC695). The most relevant studies reported in Table X are (1) the use of C CPMAS NMR to identify... 

The NMR spectrum for TsHs displays a single peak at 4.20 ppm ( /n-si = 341 Hz) characteristic of Si-H protons, while the solid state and solution Si NMR spectra each show a single peak at —83.86 and —84.73 ppm, respectively, showing that any difference in the environment of the silicon atoms (particularly in the solid state) is not resolvable. The mass spectrum of TsHs has also been reported. ... 

Besha, K., Key, C, Glimcher, M., Schimizu, M. and Griffin, R.G. 1990 Solid state carbon-13 and proton NMR studies of carbonate-containing calcium phosphates and enamel. Journal of Solid State Chemistry 84 71-81. 

A wide variety of NMR methods are being applied to understand solid acids including zeolites and metal halides. Proton NMR is useful for characterizing Brpnsted sites in zeolites. Many nuclei are suitable for the study of probe molecules adsorbed directly or formed in situ as either intermediates or products. Adsorbates on metal halide powders display a rich carbenium ion chemistry. The interpretation of NMR experiments on solid acids has been greatly improved by Ae integration of theoretical chemistry and experiment. 

So far, the majority of granular matter studies by NMR/MRI have used liquid state proton measurements in solid materials. Because proton signals are relatively insensitive to chemical environment through the chemical shift effect and because the physical environments are relatively similar in all liquids, the resonance frequency and the NMR linewidth are not good indicators of granular parameters such as particle density and velocity. 

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