Spin networks determination

The ID homonuclear Hartmann-Hahn (HOHAHA) experiment is an excellent way to determine complete coupled spin networks (18). The following pulse sequence is used ... 

One-dimensional double-resonance or homonuclear spin-spin decoupling experiments can be used to furnish information about the spin network. However, we have to irradiate each proton signal sequentially and to record a larger number of ID H-NMR spectra if we wish to determine all the coupling interactions. Selective irradiation (saturation) of an individual proton signal is often difficult if there are protons with close chemical shifts. Such information, however, is readily obtainable through a single COSY experiment. 

An approach to the determination of the orientation of the carbonyl CSA tensor in a dipolar coupled spin network has been proposed. " The... 

The INADEQUATE experiment, developed by Bax et alwill not be presented due to its lack of sensitivity, it is seldom used and this is why little will be said about its processing. A computer program called COSMIC developed by Richardz et which analyses spectra and produces carbon connectivity lists as an output is, however, worthy of mention. The introduction of pulse field gradients made it possible to design much more sensitive proton detection sequences that are quite suitable for the construction of spin networks and structure determination," even if they work only with those carbons that are directly bound to protons. 

In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). Si soHd-state nmr and chemical degradation methods have been used to characterize cured networks stmcturaHy (246). H- and H-nmr and spin echo experiments have been used to study the dynamics of cured sihcone networks (247—250). 

Increasing the length of the alkyl spacer in such a way as to yield 1,4-bis(tetrazol-l-yl)butane (abbreviated as btzb) (Fig. 16), changes the dimensionality of the Fe(II) spin crossover material [89]. In fact, [Fe(btzb)3] (C104)2 is the first highly thermochromic Fe(II) spin crossover material with a supramolecular catenane structure consisting of three interlocked 3-D networks [89]. Unfortunately, only a tentative model of the 3-D structure of [Fe(btzb)3](Cl04)2 could be determined based on the x-ray data collected at 150 K (Fig. 20). 

In order to study the cure behavior of the PTEB system, 1JC NMR of uncured and cured PTEB in the solid state was performed using crosspolarization magic-angle spinning techniques. The results show the polymerization to be via aromatization. The extent of cure versus cure temperature was determined quantitatively. It was found that the material was almost completely cured after one hour at 215°C. As the cure goes to completion, the ability to react decreases due to the corresponding rapid increase in Tg. Chemical shifts of the resonances in the cured material are consistent with a highly crosslinked condensed aromatic network. 

C This pulse sequence, the popular homonuclear 2D COSY (COrelation Speciro-scopY) experiment, was designed to determine the entire H/ H-coupling network of a molecule within a single experiment. The sequence consist of all four elements, i.e. a preparation, a evolution, a mixing and a detection period. The evolution period serves to introduce the second time (tl) domain of a 2D experiment and in the mixing period, which is actually a pulse, polarizations are exchanged among the coupled spins. 

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