Chemical shifts effect

The left-hand side of Equation (8.15) involves the difference between two electron binding energies, E — E. Each of these energies changes with the chemical (or physical) environment of the atom concerned but the changes in Ek and E are very similar so that the environmental effect on Ek — E is small. It follows that the environmental effect on E -h Ej, the right-hand side of Equation (8.15), is also small. Therefore the effect on is appreciable as it must be similar to that on There is, then, a chemical shift effect in AES rather like that in XPS. 

Dozens of compounds have been used in in vivo fluonne NMR and MRI studies, chosen more for their commercial availability and established biochemistry than for ease of fluonne signal detection [244] Among the more common of these are halothane and other fluormated anesthetics [245, 246], fluorodeoxyglucose [242 243], and perfluormated synthetic blood substitutes, such as Fluosol [246], a mixture of perfluorotnpropylamine and perfluorodecahn Results have been Imut-ed by chemical shift effects (multiple signals spread over a wide spectral range) and long acquisition times... 

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. 

The REDOR experiment (Fig. la), introduced by Gullion and Schaefer in 1989 [22], invokes a strong n pulse for one of the spin species (e.g., the I spin in an I-S spin system) in the middle of each rotor period xr - in addition to one n pulse at each rotor echo on the 5-spin channel to refocus isotropic chemical shift effects and... 

In the simplest setup, the two strong field components may be set identical to Ci = Cs = C. The relatively large CIX or CSX term averages isotropic and anisotropic chemical shift effects as well as the heteronuclear dipolar coupling interaction between 15N or 13C and H. The difference of - or the sum of - the B coefficients selects the form of the recoupled heteronuclear dipole-dipole coupling interaction, as expressed in terms of the effective Hamiltonian in the interaction frame of the rf irradiation... 

We will now proceed to provide an overview of chemical shift effects of 29Si when framework elements other than silicon and oxygen are present in zeolites. 

Fig. 19.7 Three possible orientations of the ligand HUB093 within the SI pocket of the enzyme peptide deformylase. Heavy atoms of the protein are coloured according to secondary chemical shift effects caused by the ring current...

This NMR technique has been applied to a series of alkanediammonium ions, and the results (induced shifts of proton resonances) are summarized in Fig. 2. It may be seen that the shielding region extends for approximately 4.5 methylene units, or 6 A, which coincidentally is the interatomic distance axially spanning the cavity of cucurbituril. Similar induced chemical shift effects are found in CNMR spectra, and UV spectral perturbations are noted upon encapsulation of certain aromatic-ring bearing ammonium ions (particularly 4-methyl-benzylamine). Conclusive evidence for internal complexation with cucurbituril has been secured by crystallography [3]. 

The first thing we need to consider when discussing the NMR effect is why equation (4.1) contains the term B ff rather than B. This is called the chemical shift effect, and to understand this key aspect of NMR spectra we need to consider what happens when we place our NMR sample in a magnetic field. The atomic nuclei in our sample adopt one of a number of possible alignments, depending upon their spin. We also, however, have to... 

In the application of Anet s equations (see Section II,B,5 below) to the estimation of AG and AG° by low temperature 13C-NMR spectroscopy, the magnitude of Av (the chemical shift difference between the exchanging sites) is required. Because this cannot always be observed, resort has to be made to some indirect method of estimation of Av. This has been done, for example, in the case of the l,2,4-trimethylhexahydro-l,2,4-triazine equilibrium (Section III,F,3) by estimating the chemical shifts in the various conformers from chemical shift effects based on model systems (Table VIII). Utilization of... 

C-NMR Shifts for N-Methylpiperidine,94 1,2-Dimethylhexahydropyridazine,250 1,3-Dimethylhexahydropyrimidines,289 and Chemical Shift Effects Arising from Structural Modification of N-Methylpiperidine96... 

The chemical shift effects of nitro and amino substituents are the largest normally encountered. The mildly electron donating methyl group induces far more modest shifts, as seen with 2- and 3-methylthiophene (113 and 114). 

Klinowski and Anderson (129) considered the range of the chemical shift effect necessary to account for the experimental results. They noted that nth coordination sphere rarely implies distances of the order of n x dTT, where... 

K Chemical-Shift Effects on Spin-Spin Splitting... 

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