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NMR procedure

Purity can be checked by chromatography (on thin-layer plates, Kieselguhr, paper or columns), by UV or NMR procedures. [Pg.64]

Compared with the extensive application of NMR procedures, electron paramagnetic resonance (EPR) is used less frequently except for analysis of the state of metals in enzymes and coenzymes. There has, however, been increasing awareness of the role of radical-mediated reactions and some examples are used to illustrate its potential. [Pg.288]

An NMR procedure is described by which methimazole is determined in pure and tablet formulation. The method is rapid, accurate, precise (S.d, = 0.95%) and also provides a specific identification of methimazole. [Pg.364]

The interaction of positively charged (9+) cytochrome c(III) with PCu(II) has been studied by the same NMR procedures [115]. The results obtained again indicate that there is a favorable interaction at the remote site. The corresponding interaction of PCu(II) with cytochrome f(M, 33,000) is at present more difficult to interpret without knowledge of the cytochrome f structure. [Pg.198]

Several other nmr procedures have been used for the determination of fractionation factors. These have advantages in some systems. Instead of determining the effect of the concentration of an exchanging site on the averaged chemical shift, the effect on the averaged relaxation rate of water protons can be used in a very similar way (Silverman, 1981 Kassebaum and Silverman, 1989), For example, addition of the enzyme Co(ii)-carbonic anhydrase to an aqueous solution increases the observed value of XjT because the proton-relaxation rate is the average of that for the bulk solvent (cfl. 0.3 s ) and that for water bound to the cobalt ca. 6x 10 s ). The average is different in an H2O/D2O mixture if the bulk solvent and the Cobound solvent have different deuterium contents, and it has been used to determine a value for the fractionation factor of Co-bound water molecules in the enzyme. [Pg.286]

Recently55 a 31P-NMR method for free amino acids was advanced using a reagent derived from (5)-2-butanol and phosphorus trichloride. However, a convenient H-NMR procedure has been described by Kruizinga et al.56 where Schotten - Baumann coupling of a-amino acids with (5)-2-chloropropionyl chloride, available from diazotized (S)-alanine, leads to the diastereo-meric Ar-(5)-2-chloropropionyl derivatives. [Pg.276]

At present the nmr methods are not sufficiently advanced to allow structural studies in solution to be carried out in the detailed manner in which X-ray diffraction studies are carried out. In fact the nmr procedure differs in principle from the X-ray method in that an overall picture of... [Pg.64]

Cook, R. L., Langford, C. H., et al. (1996). A modified cross-polarization magic angle spinning C-13 NMR procedure for the study of humic materials. Anal. Chem. 68, 3979-3986. [Pg.637]

Basic NMR Experiments—A Practical Course by S. Braun et al,41 describes the operation of an NMR spectrometer and, as its title implies, gives guidance, with specific experimental parameters, for carrying out a variety of NMR procedures—from measuring the width of a 90° pulse to complex pulse sequences in two- and three-dimensional NMR. [Pg.81]

Figure 9 Flow diagram of the SAR by NMR procedure. In case of completely independent binding of two ligands Left primary screening can be performed individually for each ligand. Ligands binding to two independent sites are linked, which enhances ligand-binding affinity. Figure 9 Flow diagram of the SAR by NMR procedure. In case of completely independent binding of two ligands Left primary screening can be performed individually for each ligand. Ligands binding to two independent sites are linked, which enhances ligand-binding affinity.
Safflower seed oil content can also be determined by the use of nuclear magnetic resonance (NMR), and today most plant breeders employ NMR techniques to measure their new lines. NMR techniques can be performed on only one half of a seed, so the other half can be planted if the results of the analysis are promising. In its earlier versions, processors tended to feel that NMR analysis produced oil content results that were slightly higher than found by standard solvent extraction analysis or than what was actually obtained at the oil mill. This has been disproven in the case of safflower seed, and the industry has adopted NMR analyses in large part to speed up paperwork. Because of the relatively small amount of safflower seed being measured for oil content annually, no one has taken the time to prove that present-day NMR procedures should be used to substitute for the standard AOCS procedure. [Pg.1159]

The reaction in ether resulted in a 25% yield of optically active acid 19 along with 42% of racemic hydrocarbon 15. Since the specific rotation of 19 was very small, the optical purity of the acid was determined by the more accurate NMR procedure. Hence, (S)-( —)-a-methylbenzylamide was prepared the diastereoisomeric excess determined by NMR from the signals corresponding to the cyclopropyl protons was 10%. Reaction in THF afforded a much higher yield of the Grignard reagent (58%) and only 20% of racemic hydrocarbon 15. The optical purity of the acid 19 was 13%. [Pg.71]

In recent years, attention has tended to be focused on coke deposition in zeolites (6, 7) in order to characterise the coke formed. In one specific study Groten et al (8) carried out a study of coke formation using zeolite USHY with n-hexane as reactant, but in this case, as in others (6, 7) it was necessary to deposit excessive amounts of coke (> 5%) to enable characterisation of the coke deposits to be achieved. However, if demineralisation of the catalyst is used to concentrate the coke as in the present work the inherently quantitative single pulse excitation (SPE) NMR procedure may be used to characterise coke deposits on FCC catalysts at realistic levels of ca 1% by weight. [Pg.313]

An NMR procedure was developed for the analysis of meprobamate tablets using malonic acid as an internal standard . The integrated area of meprobamate s peak at 3.8p.p.m.is compared to the integrated area of the malonic acid peak at 3 3 p.p-m. [Pg.219]

The need for scaling of the values of 3/hcoc calculated by the ab initio, DEMON-NMR procedure was assessed by comparison of the theoretical and experimental values of four 1,6-anhydro-aldohexopyranose derivatives, which disclosed that the theory overestimated the couplings by an average of 16.7%, thus leading to a scaling factor of 0.833. [Pg.40]

Compared with the extensive application of NMR procedures, EPR has been used only infrequently. Some examples are used to reveal its potential. [Pg.453]

There are a number of considerations that must be addressed when formulating quantitative 13c NMR procedures - these include solvent effects, spectral overlap, line widths, dynamic and nuclear Overhauser effects and detailed assignments. The steps required to develop sound quantitative methods will be the subject of this chapter. It is imperative that excellent quantitative methods be established so that NMR can be utilized in studies of polymer structure-property relationships. Polymer molecular structure needs to be related to the incipient solid state structure and ultimately to observed solid state physical properties such as density, flexural moduli, environmental stress cracking behavior, to name a few. [Pg.132]


See other pages where NMR procedure is mentioned: [Pg.186]    [Pg.291]    [Pg.144]    [Pg.224]    [Pg.285]    [Pg.148]    [Pg.314]    [Pg.786]    [Pg.28]    [Pg.188]    [Pg.285]    [Pg.286]    [Pg.33]    [Pg.29]    [Pg.49]    [Pg.2025]    [Pg.141]    [Pg.643]    [Pg.26]    [Pg.316]    [Pg.74]    [Pg.520]   
See also in sourсe #XX -- [ Pg.196 ]




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