Chemical shift pattern

The intramolecular stabilization of germyl cation 34 by a remote aryl substituent was demonstrated by the NMR chemical shifts of the coordinated aryl ring. The chemical shift pattern found for the coordinated arene ring of 34 is characteristic for arenium ions and it closely resembles that found bissilylated arenium ions 78. 

These conclusions can be obtained on the nonrelativistic level, and it is possible in theory to practice proton and electron spin resonance without permanent magnets, at much higher resolution, without the need for very high homogeneity, and with a novel chemical shift pattern, or spectral fingerprint, determined by a site-specific molecular property tensor, to be described later in this section. 

The absence of protonation shifts proves platination at this site, i.e. when a metal ion is coordinated at e.g. N7 of guanine, protonation cannot occur anymore at this site, resulting in the absence of a protonation pK at about pH 2. An illustration of such a pH dependent chemical shift pattern of nucleobase protons is given in Fig. 11a, b. Metal binding can also alter pKa s of sites where no metal is bound, e.g. the decrease of the pKa at Nl. 

Figure 15b shows a solid-state spectrum recorded under conditions such that only the mobile portions of the solid PDHS sample are observed. In this polymer (as previously indicated), the mobile portion of the sample consists of the locally disordered phase II and any amorphous material to the extent that it exists. The chemical-shift pattern for the carbons agrees very well with the solution spectrum (Figure 15a). Because carbon resonances are very sensitive to bond conformation (22), this result demonstrates that the phase II portion of the sample has the same average chain conformation as the polymer chains in solution. Although these NMR data permit a comparison of local bond conformations, they do not provide an indication of the more global chain dimensions. Figure 15b shows increased line widths for the carbons near the silicon backbone, with the C-1 resonance almost broadened into the baseline. This broadening reflects the severe restriction of motion near the backbone.

The 1 0 NMR chemical shift patterns for the common and not so common functional groups encountered in naturally occurring compounds provides a... 

Of importance in understanding chemical shift patterns of phenols is, of course, also the effect of taking part in hydrogen bonding as, e.g., in salicylaldehyde, o-hydroxyaceto-phenones etc. Firstly, the anisotropy caused by the OH group but also the anisotropy effects of the other substituent (aldehyde, ketone etc.) lead to extensive non-additivity if using the standard values mentioned above. 

Lastly, NMR is useful in identifying geometrical isomers when cis- and rany-double bonds are formed from polymerization of dienes such as butadiene. and ID-NMR is commonly used to distinguish between these isomeric forms, as they have distinct chemical shift patterns as shown by the spectra of cis- and rany-polybutadiene in Fig. 

Molecular shapes and 1H chemical shift patterns for chloro-ammine cobalt(III) compounds. Different environments for ammonia molecules in some complexes are defined by eq and ax subscripts, with the two types opposite different types of ligand leading to different magnetic environments and chemical shifts (8). 

Rg. 2.17 (a) A schematic representation of the generic two-dimensional NMR pulse sequence, with evolution time h, mixing period and detection time t2. (b) The separation of anisotropic chemical shift patterns for different chemical shifts (see the text), ((a) reproduced and (b) adapted by permission of Academic Press.)... 

Carbon chemical shifts. The chemical shift patterns in the NMR spectrum of a polymer with chiral centres usually contain much more detailed confor-... 

Due to chemical shift dispersion, considerable overlap occurs, as is evident via an inspection of the results in Table 2 and the experimentally observed chemical shift patterns (Figure 1). Therefore only three peak regions can be discerned and subsequently assigned (the number between brackets indicates the level of hydrogen bonds) ... 

Hydroxyquinoline carboxylic acids and their conjugate acids and bases were characterized by C and N NMR spectroscopy in solution and in the solid-state. It was found that differences in C and, in particular, N chemical shift patterns allow to distinguish between individual tautomers and confirm the presence of zwitterionic species in the solid-state. Solution NMR spectra in DMSO-Jg showed effects resulting as a consequence of dynamic exchange and suggest the presence of an equilibrium mixture of hydroxyquinoline carboxylic acid and zwitterionic hydroxyquinolinium carboxylate tautomers. 

Identical chemical shift patterns, however, were obtained on samples run... 

The C-n.m.r. spectra of various glycosides of a- and -L-arabinofuranose [e.g. monosaccharides (3) and glucosylated derivatives such as disaccharide (4)] have been assigned, and chemical shift patterns characteristic of certain types of... 

Resonances were not assigned by original authors present tentative assignment based on chemical shift patterns of similar types of compounds reported in this review. 

Chart 2. Chemical Shift Patterns in Organotin Compounds. 

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