Nuclear magnetic resonance spectrum integration

The structures of vanicosides A (1) and B (2) and hydropiperoside (3) were established primarily by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques and fast atom bombardment (FAB) mass spectrometry (MS).22 The presence of two different types of phenylpropanoid esters in 1 and 2 was established first through the proton (4H) NMR spectra which showed resonances for two different aromatic substitution patterns in the spectrum of each compound. Integration of the aromatic region defined these as three symmetrically substituted phenyl rings, due to three p-coumaryl moieties, and one 1,3,4-trisubstituted phenyl ring, due to a feruloyl ester. The presence of a sucrose backbone was established by two series of coupled protons between 3.2 and 5.7 ppm in the HNMR spectra, particularly the characteristic C-l (anomeric) and C-3 proton doublets... 

Use of an integrated system incorporating CCC separation, PDA detector, and LC-MS proved to be a valuable tool in the rapid identification of known compounds from microbial extracts.6 This collection of analytical data has enabled us to make exploratory use of advanced data analysis methods to enhance the identification process. For example, from the UV absorbance maxima and molecular weight for the active compound(s) present in a fraction, a list of potential structural matches from a natural products database (e.g., Berdy Bioactive Natural Products Database, Dictionary of Natural Products by Chapman and Hall, etc.) can be generated. Subsequently, the identity of metabolite(s) was ascertained by acquiring a proton nuclear magnetic resonance ( H-NMR) spectrum. 

It is unreahstic to attempt the use of the Fourier series or of the Fourier integral transforms without the aid of a computer. In recent years a fast Fourier transform (FFT) algorithm for computers has become widely used. This is particularly useful in certain kinds of chemical instrumentation, specifically nuclear magnetic resonance and infrared absorption spectrometers. In such instruments the experimental observations are obtained directly in the form of a Fourier transform of the desired spectrum a computer that is built into the instrument performs the FFT and yields the spectrum (see Chapter XIX). 

Nuclear magnetic resonance (NMR) spectroscopy is regarded as one of the most important analytical techniques in chemistry for characterization of molecular structure. In addition to the structural information, NMR spectroscopy also gives quantitative information about the sample constituent. The induced current in the coil can be regarded as linearly dependent on the concentration of the nucleus in the sample. Therefore the resonance integrals in a simple one-dimensional spectrum measured with the excitation-acquisition scheme offer a way to measure absolute amounts of the chemicals present in the sample. Recently, the need for quantitative analysis of highly complex samples has led to a situation where resonance overlap in... 

Molecular dynamics attempts to solve the dynamically evolving ensemble of molecules given the interactions between molecules. The form of the forces between molecules or atoms, the number of interactions (i.e., two- or three-body interactions), and the number of molecules that can be tackled by the program determine the success of the model. Molecular dynamics simulations can predict the internal energy, heat capacity, viscosity, and infrared spectrum of the studied compound and form an integral part in the determination and refinement of structures from X-ray crystallography or nuclear magnetic resonance (NMR) experiments. 

Figure 3.22 The power distribution for a 10 ps rectangular pulse of 500 MHz RF radiation, (a) Distribution over a 400 kHz range, (b) The power level drops to 97% of the maximum at 5 kHz (10 ppm) on both sides of the center of the spectrum. This can affect the accuracy of integrals for resonances in different regions of the spectrum. (From Petersheim, M., Nuclear magnetic resonance, in Ewing, G.A., ed.. Analytical Instrumentation Handbook, 2nd edn., Marcel Dekker, Inc., New York, 1997. Used with permission.)...

The instructor or a laboratory assistant will record the NMR spectrum of the reaction mixture. Submit a sample vial containing the mixture for this spectral determination. The spectrum will also contain integration of the important peaks (Technique 21, Nuclear Magnetic Resonance Spectroscopy). 

Co-crystal patents usually contain experimental examples that describe the preparation of the co-crystal and the characterization of the co-crystal. Characterization of the co-crystal describes the co-crystal itself and its various properties which include its sohd state characteristics and stoichiometry. Typically, the sohd state characteristics of a crystalline solid are shown by one or more of the foUowing analytical techniques X-ray powder diffraction pCRPD), single crystal X-ray diffraction (SCXD), Raman spectroscopy, infrared (IR) spectroscopy, sohd state nuclear magnetic resonance spectroscopy (SSNMR), and differential scanning calorimetry (DSC). The stoichiometry of a co-crystal may be estabhshed through solution techniques such as comparison of peak integrations in a solution NMR spectrum, data... 

For ordinary paramagnetic substances the integrated area under an ESR spectrum is proportional to the number of spins in the paramagnetic species producing the resonance line. In a multicomponent line the number of hyperfine components provides the magnitude of the nuclear spin. The g factor is a measure of the orbital contribution to the spin magnetic moment, and it is frequently possible to identify a particular valence state of an ion by its g factor. In chromia-alumina the valence states of Cr + and Cr + have been detected by ESR. 

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