Line-broadening effects

Each vibrational peak within an electronic transition can also display rotational structure (depending on the spacing of the rotational lines, the resolution of the spectrometer, and the presence or absence of substantial line broadening effects such as... 

The widespread occurrence of long-range couplings in both furanose and pyranose derivatives explains why so many of the P.M.R. spectra of carbohydrate derivatives are apparently poorly resolved, even when the resolution of the spectrometer is above reproach. For example, the Hi resonance of the 1,6-anhydro-D-glucose derivative (12) is coupled to all of the other six ring protons. A further example of the line-broadening effect follows a consideration of the spectrum of 5,6-dideoxy-5,6-epithio-l,2-0-isopropylidene-/ -L-idofuranose for which the half-height... 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

The NMR investigation is presented in two parts the first covers i3C 99rpc ancj i5N studies where protonations of the dioxo complexes induce chemical shift changes but where line-broadening effects due to exchange are not observed. The second part covers 170 studies which produce more complicated spectra due to protonation and simultaneous exchange with bulk water. 

The analysis of a full tilt series of 2H NMR spectra not only allows the determination of the unique bond angle for a deuteriated methyl group, but also provides an internal check for the consistency of the spectral interpretation. In particular, simulations provide a means for the analysis of line-broadening effects, which arise from the sample mosaic spread as well as the intrinsic line width of the nuclear transition and instrumental factors. When line shapes are fitted to a full tilt series of spectra in a concerted manner and are also compared with the powder spectrum of an unoriented sample, the different contributions can be discerned. In that way an intrinsic line width of around 2 kHz is found for the spectra shown here, together with a mosaic spread between 8° and 10° for the three samples. 

Characterization of the modified plastocyanins was by Inductively Coupled Plasma Emission Spectroscopy to analyze for Ru and Cu (1 1 ratio), and by HNMR spectroscopy. In the HNMR characterization the C2H resonance of His59 at 8.2 ppm is seen to be lost due to paramagnetic line broadening effect of the attached Ru(III), Fig. 13 [50]. In a further test it is known that the His59 s of both native plastocyanins react with diethyl pyrocarbonate (DEPC) to give an JV-ethoxyhistidine derivative, (12), which absorbs strongly at 238 nm (e 2750M- cm-i), Fig. 14 [133]. 

Line-broadening effects for nitroxide-functionalized dendrimers that have unreacted primary amines and line-broadening effects when a second isothiocyanate is reacted with the dendrimer do not vary significantly. One clear indication of... 

What, then, is the end-group pattern that emerges from sequential addition of reactive components We calculated the expected line-broadening effects for randomly functionalized dendrimers and compared them to the experimentally observed linebroadening effects. Figure 13.18 compares the experimental results from the stackplot in Figure 13.16 to the calculated results. Because a wide body of hterature now indicates that dendrimer end groups can backfold into the interior of the dendrimer (Ballauff and Likos 2004), we included a volume shell in our calculations. 

Figure 13.17 Graph of line-broadening effects for 2,2,6,6-tetramethylpiperidine A -oxide (TEMPO) and R-4-isothiocyanato (R-NCS) functionalized dendrimers from Figure 13.15. NCS-TEMPO was added first half of the time and R-NCS was added first half of the time.

TABLE 13.1 Comparison of Calculated Line Broadening Effects with Experimentally Determined Line Broadening Effects of PROXYL Functionalized Dendrimers... 

The ESR spectra of a series of triarylboron anion radicals have been determined and show selective line-broadening effects (95). The radical anions of diborane, generated in an argon matrix at 77 K by irradiation with a-rays have been studied by ESR (121). The vanadium-aluminum complex obtained on mixing dichlorobis(7r-cyclopentadienyl)vanadium with ethylaluminum dichloride, a system that catalyzes the polymerization of ethylene to give a polymer with good characteristics, has been characterized by ESR and ultraviolet studies (44). 

As a consequence of the line broadening effects of internal magnetic interactions on solid-state NMR spectra (Section ILA), experiments that characterize working solid catalysis require the application of the MAS technique. Because of the salient feature of MAS NMR spectroscopy (rapid sample spinning during the measurement), specific techniques had to be developed to allow characterization of solids in sealed vessels under batch reaction conditions and in fixed-bed reactors under flow conditions. 

Due, in the main, to quadrupolar line-broadening effects, together with the poor sensitivity, there has been relatively little general interest in 14N magnetic resonance studies and, although the quadrupolar broadening has been shown to be minimized by the use of low viscosity solvents,465 the 14N chemical shifts of only four pyrroles have been reported.465,466 The 14N chemical shift of pyrrole has been reported as either 230465 or 227466 ppm relative to the N02 ion 14N resonance, and values of 227, 230, and 225 ppm have been recorded for 1-methylpyrrole, 2,5-dimethylpyrrole, and l-methyl-2-methoxy-carbonylpyrrole, respectively.465 The associated effect of electric... 

Vary the temperature in order to get an optimum balance between competing line-broadening effects. 

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