Spectrum shift

Proton chemical shift spectra over the range of 0—15 ppm ( 0.1 ppm) TFA, ttifuoroacetic acid DMSO, dimethyl sulfoxide. When complex spectra caused by second-order effects or overlapping resonances were encountered, the range was record (11,12). 

Estimated precision in the chemical shifts is 0.05 p.p.m. The chemical shifts are given relative to external 1,4-dioxane, which was introduced into some samples only to obtain chemical shifts. Spectra obtained at 258 for — 10% solutions. Spectra of compounds were obtained at 22.5 MHz see Ref. 20. Spectra of compounds were obtained at 22.5 MHz see Ref. 24.J Spectrum obtained at 100.6 MHz see Ref. 24. Data taken from Ref. 61. Chemical shifts for GalNAc only are given. The data given in the parentheses for compounds 51 and 32 refer to the carbon count. 

We see that as spectral width is increased, the spectra have to be shifted to longer wavelengths to maintain the proper X/Y ratio, otherwise the short wavelength wing would yield an orange color shift. This has the disastrous consequence, however, of drastically reducing the values of X and Y, since the broadened, shifted spectra make increasingly poorer matches to the x and y curves. 

In addition to red-shifted spectra and low rotational amplitude, Ehrlich ascites plasma membranes exhibit Cotton effects in the region of aromatic chromophores, 250-300 m/ (89). Similar behavior has been observed in other proteins, such as carbonic anhydrase (34) and lysozyme (58), and disappear upon denaturation. Ehrlich ascites plasma mem-... 

Fig. 13.7. Scatter plots of linear re-shifted spectra superimposed over original model. Top re-shift 2cm 1, bottom, re-shift 5 cm-1. Solid markers are original model and hollow markers are the shifted data. Black triangles are group centroids...

As regards the aliphatic carbons, the chemical shift spectra of MGIM76 at various temperatures are shown in Fig. 153, as well as the NMR spectrum obtained for MGIM76 in solution. As for C = O(MGI) groups, spectrum shape changes only occur between 115 and 160 °C. Two spectrum regions are concerned ... 

When Con,-EDDA-complexes are synthesized under conditions favoring equilibrium state, the cis-a-compound is essentially obtained72. Cis-(3-complexes can also be obtained, most favorably as mixed ligand complexes with a bidentate ligand, e.g. carbonate, oxalate or 1,2-diamines73-75. But in all cases known, it is the cis-a-isomer which is formed in a greater amount. Reilley and co-workers conclude from the simplicity of the NMR-contact shift spectra of [Ni(EDDA)(H20)2] that the compound is present in only one isomeric form, and assume that this is the ezs-a-form28. ... 

Variable temperature (-150° to +350°) chemical shift spectra have been obtained for melt-recrystallized samples of PTFE. The NMR spectra were acquired using the REV-8 sequence which consists of a long train of closely spaced, high power rf pulses of fixed width, and varying in phase in a cyclical fashion. The cycle consists of eight ir/2 pulses. The total cycle time used was 43.2 psec with a shortest spacing between pulses of 3.6 usee. The nominal resonance frequency was 84.6... 

Chemical shift spectra of PTFE obtained at 259° are shown in Figure 1. These lineshapes, for three different samples of varying crystallinity, may be seen to be a linear combination of two lineshapes one is characteristic of an axially symmetric powder pattern and the other of an isotropic chemical shift tensor. At this temperature these two lineshapes differ greatly and may be numerically decomposed. 

Figure 1. F-19 REVS chemical shift spectra of PTFE samples of varying...

It is clear from the chemical shift spectra that the only process observable in the crystalline regions from -128° to +320° (near the melting point) is reorientation about the chain axis. Translational displacements along the chain axis in well-ordered crystalline regions (which have been previously observed—-—) would not give rise to any observable change in the chemical shift spectra. However, the chemical shift spectra of the... 

The numerical method used to decompose the chemical shift spectra are detailed in a paper submitted to Macromolecules. 

I found that the philosophy behind making the TCM-HABI—Could we use less costly ingredients, shift spectra, increase stability, etc.—required an approach toward chemistry that depended on synthesis to solve problems. Most industrial photochemists are better at formulating around deficiencies, and so it was at DuPont Once o-Cl-HABI was available, the formulators worked around it. Only when a special problem arose, such as the need for a less colored photoinitiator, was an effort made to develop new compounds After all, one cannot readily add a compound that would make a yellowish compound white Hence, the work that resulted in the 2-(alkyloxy)-4,5-diphenylimidazole dimers. 

Useful for Raman shift spectra (0-2,400 cm-1 region) obtained by 632.8-nm excitation of a He-Ne laser. 

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