Integration of nmr spectra

Applications of NMR spectroscopy to structural, thermodynamic, and dynamic processes have been described. A brief discussion of the types of problems appropriate for study by this technique has been included. H and 13C NMR spectroscopy has been applied to define the ligand coordination in complexes. These experiments, combined with 170-labeling experiments, allowed deduction of the coordination number of the vanadium atom. Integration of NMR spectra allowed measurement of the formation constants and equilibrium constants. 2D 13C and 51V EXSY experiments were used in a qualitative and quantitative manner to examine intra- and intermolecular dynamic processes, of which several examples are discussed. The interpretation of the rate matrix and its relationship to the chemical processes under examination were also described. 2D EXSY spectroscopy has great potential as a tool with which to probe mechanisms in complex reactions however, such uses often requires estimation of errors. The major source of error in 2D 51V EXSY NMR studies on a two- and four-site vanadate system were found to be baseline distortion and the errors were estimated. Our results suggest... 

Analysis. The liquid clathrates were analyzed by the integration of NMR spectra recorded on a Perkin-Elmer R20-B instrument. The aromatic stoichiometries in Table II are in most cases the average of three preparations and integrations a realistic standard deviation would be 0.2 molecules. The chemical shifts are accurate to better than 0.02 ppm. 

Molar miscibility and saturation point measurements describing liquid clathrate behavior are commonly analyzed by the integration of NMR spectra. In most cases, the aromatic stoichiometries are the average of three preparations and integrations with an acceptable standard deviation result of 0.2 molecules. A common feature of all liquid clathrate NMR spectra is the shifting of the entire spectrum 0.2-0.5 ppm downfield relative to the pure aromatic substance. 

The enantiomers of camphorcarboxylic and sulfonic acids are used for resolution of enantiomers from racemic chiral amines and alcohols via diastereomeric salts and esters, respectively. Europium(III)- and praseodymium(III)-chelates of hydroxy-methylenecamphor derivatives are suitable chiral shift reagents for the determination of enantiomeric purity by integration of NMR spectra, because they exchange ligands with enantiomeric substrates such as alcohols and amines, thus forming diastereomeric chelates characterized by different spectra. 

Infrared and Raman spectra contain information about what compound(s) could be present in a sample and about the relative amounts of such constituents, as well as giving insights into the stmctures of compounds. Determination of rotation constants from high-resolution spectra of gases is described in Section 7.3.2, and derivation of force constants is discussed in Section 8.9. Absolute quantitative measurements of concentrations, such as can be obtained by integration of NMR spectra, are not possible for unknown species, because the intensity of each IR or Raman band for each compound is a specific property of that molecule. We have seen that the shapes and positions of bands vary depending on the phase of the sample, but even so the overall profile of absorption (or transmission) of a spectrum can be analyzed as a function of the relative concentrations of the components of the sample, if reference spectra for each of the components are... 

Chapter 13—Structure Determination Nuclear Magnetic Resonance Spectroscopy. Integration of NMR spectra is presented in a digital format rather than in the outdated stair-step format. 

Wlien Al MAS NMR spectra were first collected at moderate Bq with relatively slow MAS rates (<4 kHz) there was much confiision about the quantitative integrity of such spectra. In fact, provided the correct excitations are employed (i.e. and 1) all that is necessary to make MAS NMR spectra... 

The ability of the stable carbene 218 to deprotonate acidic hydrocarbons was examined by NMR in (CD3)2S0.153 Indene (pJta = 20.1) was completely converted to its anion whereas 9-phenylxanthene (pAfa = 27.7) was not measurably deprotonated. The NMR spectra of 1 1 mixtures of 218 with fluorene (pXa = 22.9) and 2,3-benzofluorene (pA"a = 23.5) showed separate absorptions for the hydrocarbons and their anions. From the integration of these spectra, P a = 24.0 for 218 was derived. In THF, 218 failed to deprotonate fluorene but almost completely deprotonated indene. The proton transfer from hydrocarbons to 218 creates ions (ion pairs) from neutral species, which will be less favorable in solvents of lower polarity. 

HyperChem Release 7 , available in 2002, is a full 32-bit application, developed for the Windows 95, 98, NT, ME, 2000 and XP operating systems. Density Functional Theory (DFT) has been added to complement Molecular Mechanics, Semi-Empirical Quantum Mechanics and Ab Initio Quantum Mechanics already available. The HyperNMR package has been integrated into the core of HyperChem, allowing for the simulation of NMR spectra. A full database capability is integrated into HyperChem 7. Many other features are updated and improved. 

As mentioned earlier, the irradiation of directly bonded hydrogen atoms increases the intensity of C signals through the NOE, which means that CH, CH2 and CH3 groups usually have a relatively high intensity in a NMR spectrum, while we can often recognize quaternary carbon atoms because of their low intensity. This difference in intensity is due to the different relaxation rates, and is the reason we do not integrate C NMR spectra. 

This mixture is recrystallized three times with the same mixture of solvents and the product Is collected after 1 hr at 0°C to give 8.7 g (47.9%, mp 101-103°C) of a 25 1 mixture of diastereoisomers (values based on the 8a-methyl signal integration on NMR spectra) (Note 15). 

However, the detailed studies of NMR spectra led to the conclusion about the interchange of apical and equatorial fluorine atoms. Since the apical and equatorial bonds P—F in PF5 have different lengths, the NMR spectrum can be expected to consist of two doublets with integral intensity ratio 2 3. Actually, the observed NMR spectrum of PF5 (at F) has one doublet caused by spin-spin interaction of P and F nuclei, i.e. the splitting of signals from axial and equatorial fluorine atoms is absent. 

The basic problem in the interpretation of NMR spectra of humic substances is that for quantitation, as we have pointed out above, the integrated area under a given band in a NMR spectrum is not only a function of the number of carbon atoms resonating at that frequency, but is also a... 

One of the prerequisites for automatic use of NMR spectra as descriptors to enable sample classification has been the need to reduce the spectra to a series of multidimensional coordinates. One way is to segment the spectrum and integrate over each segmented region, thereby removing the effects of minor chemical shift changes as a result of changes, e.g. in pH. ... 

Volatile peptide derivatives, for instance trifluoroacetyl-L-valyl-L-valine methyl ester or benzyloxycarbonyl-L-leucyl-L-phenylalanyl-L-valine tert.butyl ester can be separated from their diastereoisomers that contain a D-residue by vapor phase chromatography. Also, through the examination of nmr spectra of relatively simple peptides the extent of racemization that occured during their preparation can be determined without separation of the diastereoisomers, because the difference in the chemical shifts of some selected resonances is sufficient for integration. Thus the areas under the well separated peaks of the alanine methyl protons in acetyl-L-phenylalanyl-L-alanine methyl ester and in acetyl-D-phenylalanyl-L-alanine methyl ester can be integrated and the values used to determine the extent of racemization of the phenylalanine residue during coupling. 

Fig. 3.30 Resonant frequency of black squares) and (white squares) dependence on mean particles size. Symbols are experimental data, solid line represents the calculations on the base of Eq. (3.99) with parameters for too = 47.5 ppm, k = 6.5 ppm nm. Ho = 40.18 MHz for Mg coq = 26 ppm, = 10 ppm nm, Ho = 18.3 MHz. Inset size dependence of the ratio of NMR spectra integral intensity to the whole spectra. Solid line is calculation by the expression Ic/I = 1 — (1 — AR/Rq) at AR = 0.3486 nm, black and white triangles are fitting parameters and NMR spectra experimental points respectively [105]...

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