NMR parameters

NMR spectra can be described using an effective Hamiltonian of the form 

The use of fcM the shielding tensor is conventional but unfortunate in this connection due to the notational similarity to the Pauli cr matrices. H e, the shielding tensor will always have a capital letter subscript, mid it only appears in this section, so die chances of confusion should be minimal. 

To obtain the quantities ok and Kkl from electronic structure calculations, we turn again to response theory. From the form of the effective Hamiltonian it is evident that 

If we use the Hamiltonian (13.41), we have no terms that are quadratic in the response parameters B and Ik, and the only contribution to the second-order perturbation energy comes from the sum over states 

The first term in the sum for the shielding constants may be split into the contribution from the negative-energy states and the positive unoccupied states 

These have been summarized previously and are relatively few. A selection of the earlier values are given together with those from some more recent publications in Table Some mixtures of molten Inij-In have been examined. The In shifts 

It is appropriate here to compare the linewidths of the three elements so far considered and see if these follow the sequence given in Table 1. It has already been noted that some gallium resonances seem broader than expected, and the early work with indium gave rise to similar conclusions that exchange processes may be important for these heavier elements or that the coordination may differ from that assumed and 

Compound/solvent Chemical shift (ppm) Other information Reference 

InCl /various 415 80 Width 180 Hz in CH2CI2 broader in other solvents 219-222 

Note that the value for Ga is based on a Tj determination, whereas the linewidth is 252 Hz. For In, the value quoted is the minimum observed. 

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I. Ando, G. A. Webb, Theory of NMR Parameters Academic Press, London (1983). 

Table 1. Nmr Parameters for Less Commonly Used Nuclei 10 ...

Compound CAS Registry Number Boiling point, °C Density at 20°C, g/cm Dipole moment, 10-"° Cm Index of refraction, < PR nmr Parameters chemical t shift, ppm ... 

Another principal difficulty is that the precise effect of local dynamics on the NOE intensity cannot be determined from the data. The dynamic correction factor [85] describes the ratio of the effects of distance and angular fluctuations. Theoretical studies based on NOE intensities extracted from molecular dynamics trajectories [86,87] are helpful to understand the detailed relationship between NMR parameters and local dynamics and may lead to structure-dependent corrections. In an implicit way, an estimate of the dynamic correction factor has been used in an ensemble relaxation matrix refinement by including order parameters for proton-proton vectors derived from molecular dynamics calculations [72]. One remaining challenge is to incorporate data describing the local dynamics of the molecule directly into the refinement, in such a way that an order parameter calculated from the calculated ensemble is similar to the measured order parameter. 

Table 1 Interactions in solid state NMR, parameters, their selective measurement, and...

The rehability of these analytical methods may be questionable when chemical shift differences of derivatives are of the same magnitude as variations encountered from solvent, concentration, and temperature influences. Reported fluorine chemical shift ranges for tnfluoroacetylated alcohols (1 ppm), p-fluorobenzoylated sterols (1 ppm), and p-fluorobenzoylated ammo acids (0.5 ppm) are quite narrow, and correct interpretation of the fluonne NMR spectra of these denvatized mixmres requires strict adherence to standardized sampling procedure and NMR parameters. 

Tire and NMR parameters of some 1-alkyl-4-benzimidazolyl-2-idene- (type 72) and l-alkyl-4-(5-methylpyrazolyl-3-idene)-l,4-dihydro pyridines (type 73) were discussed in 89CC1086 and 91JOC4223. Comparison of the shifts for DMSO-dg and CDCI3 solutions with data reported for quaternary pyridinium compounds as well as anionic species in the azole series and data obtained for mesoionic betaines of the azinium azolate class left no doubt that these heterofulvalenes have a betaine character and, therefore, the NMR signals correspond to their dipolar resonance form. 

Table 3 Individual NMR parameters (c5, J) calculated for different hydrolytic species of [Me2Sn(IV)] " (Ref 54) and [Et2Sn(IV)] " (Ref 55)...

From the NMR spectra of MeiSnCli solutions recorded at different values of pH, considering the known species distribution of hydroxo complexes in fast mutual exchange, it is possible to calculate the individual NMR parameters 6, )... 

Band L, Bencini A, Benelli C, Gatteschi D, Zanchini C (1982) Spectral-Structural Correlations in High-Spin Cobalt(II) Complexes. 52 37-86 Band L, Bertini I, Luchinat C (1990) The H NMR Parameters of Magnetically Coupled Dimers-The Fe2S2 Proteins as an Example. 72 113-136 Baran EJ, see MuUer A (1976) 26 81-139... 

The proton spectra of thietane oxide (5a) and thietane dioxide (5b) have been studied in order to evaluate whether the oxidation at the sulfur atom changes the established 35° puckering of the ring , and whether a correlation is possible between structure and NMR parameters . 

The results of NMR measurements have to be converted into a 3D structure. After establishing the constitution by NMR parameters that are transmitted through bond, i.e. J-coupHng constants, information about the spatial structure is introduced. Here, mainly distances from NOE build-up rates are used to define the configuration and conformation. 

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