CP/MAS technique

The chemical shifts are for the solid state spectra obtained by the CP-MAS technique and referred to hexamethyl benzene (132.3 ppm compared to TMS). 

Fig. 1. 13C-NMR fast exchange-slow exchange transition for the conformational interconversion of cyclododecane in solution of propane-d, (left side) and in the solid by CP-MAS techniques (right side) at 75.47 MHz. The temperature decreases from top to bottom as indicated at the spectra. Chemical shifts are given at the signals and refer to TMS = 0 ppm. (Ref.7))...

With an understanding of magnetic interactions in the solid state, inherent relaxation processes, and experimental techniques to overcome these difficulties, Schaefer et al. acquired the first liquid-like NMR spectrum of a solid by CP/MAS techniques [27]. Before a review of recent applications of CP/MAS NMR to the pharmaceutical sciences, the brief Experimental section details some important information regarding practical solid state NMR. 

The C chemical shifts of benzotriazole in the solid state are obtained using the CP-MAS technique. The chemical shifts are slightly different from those observed in DMSO-dg or CDCI3 <83H(20)1713>. CP-MAS C NMR spectroscopy is a powerful tool which enables determination of the tautomeric structure of benzotriazole in the solid state. Thus, the solid-state C NMR spectra of some A-(dialkylaminomethyl)benzotriazoles support the existence of only the N(l) isomer <87JCS(P1)2673>. 

We have employed CP/MAS techniques for characterizing two sets of coal macerals. In the first set, we examined eight maceral samples (two alginites, two sporinites, three vitrinites and one fusinite) of Carboniferous and Permo-Carboniferous age which have been previously reported (14). We now compare this work with a set of six hand picked vitrinite macerals from the Lower Kittaning seam. 

The dehydrohalogenation products of poly(ethylene-a/z-chlorotrifluor-oethylene) were also studied using solid-state NMR spectroscopy and the cross-polarization magic angle spinning (CP MAS) technique [18]. The elimination reaction induced by potassium ZerZ-butoxide (z-BuOK) in tetrahydrofuran (THF) was found to proceed slowly only 50% of hydrogen... 

In the solid state, high-resolution Sn NMR spectra can be readily obtained, in most cases, by using CP/MAS techniques, based on an optimized contact time (see Fig. 4) or by using variable contact times. Owing to the high NMR sensitivity, even single-pulse techniques will provide meaningful Sn NMR spectra within reasonable time. 

Typically, PA is synthesized as the m-isomer and the fran -isomer can be obtained from the cw-isomer by heating. The first NMR measurement on polyacetylene was carried out by Maricq et al. [2] by the CP/MAS technique. The chemical shift positions differ by 10 ppm the peak position of the frans-isomer is 139 ppm and the ds-isomer is 129 ppm. Gibson et al. studied the isomerization of the cis- to fran -polyacetylene by heating. As shown in Fig. 16.1, the sample without heating showed only one peak (128.5 ppm) which is characteristic of ds-polyacetylene. By isomerization at high temperature, a tram-peak appears at 137.3 ppm. It is weak at first but increases in intensity as the heating continues. Finally, the ds-peak disappears completely. Terao et al. [3] found that at the middle stage of isomerization, the tram-peak position shifts to low frequency with respect to that of a... 

The Ti measurements of polymer gels are carried out by an IR method combined with the PST/MAS or CP/MAS techniques. The pulse sequence for the IR combined with the PST/MAS is shown in Fig. 20.1(b). In the pulse sequence, a tt pulse and a recovery time x are inserted and the recovery time is changed in series to measure Ti. 

It is now obvious that NMR is a unique technique for the analysis of both the conformation and dynamics of polysaccharides in solutions, solids and gels. Especially, it is very useful to distinguish between the liquid- and solid-like domains by use of DD- and CP-MAS techniques. In addition, a systematic study of a converison diagram among polymorphs by a series of physical treatments is especially useful in order to clarify whether the polysaccharide chain under consideration takes a single or multiple chain both in the solid and in the gel. 

Schaefer et al. acquired the first liquid-like NMR spectrum of a solid by CP/ MAS techniques (23). 

A Naito, S Ganapathy, K Akasaka, CA McDowell. Spin-relaxation of carbon-13 solid amino acids using the CP-MAS technique. J Magn Reson 54 226-235, 1983. 

In general, l3C CP/MAS techniques depend on the mathematical manipulation which is employed to enhance the resolution of solid state NMR coal spectra.27 The several methods that have been implemented include ... 

Solid-state 207Pb NMR spectra can be obtained for static samples or by MAS and CP MAS techniques,19 and for organolead compounds CP MAS techniques are definitely preferred (see Fig. 3). The huge chemical shift anisotropy is a drawback for all techniques, although, on the other hand, this parameter contains valuable additional information. 

---