Nuclear magnetic resonance chemical identity

Enantiomers have identical chemical and physical properties in the absence of an external chiral influence. This means that 2 and 3 have the same melting point, solubility, chromatographic retention time, infrared spectroscopy (IR), and nuclear magnetic resonance (NMR) spectra. However, there is one property in which chiral compounds differ from achiral compounds and in which enantiomers differ from each other. This property is the direction in which they rotate plane-polarized light, and this is called optical activity or optical rotation. Optical rotation can be interpreted as the outcome of interaction between an enantiomeric compound and polarized light. Thus, enantiomer 3, which rotates plane-polarized light in a clockwise direction, is described as (+)-lactic acid, while enantiomer 2, which has an equal and opposite rotation under the same conditions, is described as (—)-lactic acid. 

Control analyses rely on the use of appropriate procedures or measurements assuring the identity of the materials involved in each step of the manufacturing process from receipt of raw materials to delivery of the finished products. NIR spectroscopy is an advantageous alternative to wet chemical methods and instrumental techniques such as IR, Raman and nuclear magnetic resonance (NMR) spectroscopies for positive identification. 

Identification of unknown compounds by retention times or peak enhancement is not conclusive or absolute proof of identity. It is possible for two different substances to have identical retention times under the same experimental conditions. For positive identification, the sample must be collected at the exit port and characterized by mass spectrometry, infrared, nuclear magnetic resonance, or chemical analysis. 

The chemical aspects of these studies focus primarily on the chemical characterization of the test substance and/or mixture. The identity of the test chemical should be proven, and the analytical procedures used, such as gas or liquid chromatography, nuclear magnetic resonance spectrometry, or nass spectroscopy, should be available for audit. This would include the chromatograms or spectra from these analyses. It is imperative that raw data be left intact as they emerge from an instrument to maintain data integrity. Chro-natographic printouts are to remain attached and in sequence. If some data points are not used in the final report, the reason is to be documented and those not used are to remain with the stud/ file. 

So far, only one detailed discussion of boron-11 nuclear magnetic resonance spectra of aminoborane systems has been reported 31>. It was found that the 1 lB chemical shifts of aminoborane systems can be described fairly well in terms of a set of additive substituent contributions. In consonance with earlier work on trisubstituted boron compounds 35> these contributions depend on the mesomeric effects of substituents rather than their electronegativity. 1,3,2-diazaboracycloalkanes can be considered as aminoborane derivatives and in the case of the known heterocycles the exocyclic boron substituent will govern primarily the boron chemical shifts and will do so by mesomeric effects. However, the available data are rather limited and it may be possible that additional factors must be considered. Steric effects appear to be negligible, however, since the heterocycles with either six or seven annular atoms have almost identical shifts (Table 5). 

The nuclear magnetic resonance spectra of certain pyrazoles have been studied.130 Somewhat paradoxically the hydrogen atoms in positions 3 and 5 of N-substituted pyrazoles have the same chemical shifts, though they are by no means identical chemically. (On NMR spectra of pyrazoles see also references 130a, 1306, and 130c.) It has been shown that 1,3-dialkylpyrazoles are stronger bases than the corresponding 1,5-isomers.19,44 For other physical properties, see references 131-133. 

The wide line fluorine nuclear magnetic resonance of the intercalation compound "CifcBFV may be used not only to demonstrate the chemical identity of the inserted species but also to establish the translational freedom of this species. The chemical shift of the fluorine resonance is at (70+10) ppm vs. CF3COOH, consistent (11) with BF4 (71 ppm) but not with BF3 (54 ppm). (The neutral/ anion complex, B2 7> is also possible (12)). The derivative extremum llnewldth is narrow (0.02 mT = 800 Hz) at all temperatures between -168°C and 23°C. A simple calculation suggests that translation, and not rotation, is the cause of this narrow line. Assuming a first stage compound (as indicated by X-ray diffraction)... 

Once a separation is developed, several pieces of information about the sample can be ascertained from the chromatogram. First, by counting the peaks, one can estimate how many components are present in the mixture. Second, by the use of standards, both the identity and concentration of each compound present can be obtained. Lastly, if the mixture is totally unknown, the peaks can be collected and the identity confirmed by other instrumental methods of chemical analysis (e.g., infrared, nuclear magnetic resonance, or mass spectroscopy). 

Extracts of pure proanthocyanidins have been prepared using reversephase and adsorption chromatography, and their identity confirmed with 13C nuclear magnetic resonance imaging, ultraviolet spectroscopy, and chemical reagent tests (Howell and Vorsa, 1998). 

Recurrent hepatitis was reported in a 5-year-old girl who had taken 3 tablets daily of shou wu pian, a product made from fo-ti tuber, for 4 months. Elevated serum levels of bilirubin and liver enzymes were observed, and viral markers were used to rule out a number of diseases. Symptoms disappeared and liver function tests were normal 1 month after cessation of the product. The girl experienced hepatitis again after being administered 2 tablets daily of the same product for 1 month (Panis et al. 2005). The product identity was confirmed by nuclear magnetic resonance analysis and showed 2,3,5,4 -tetrahydroxystilbene-2-O-P-D-glucopyranoside, a stilbene glycoside, to be the main constituent. The anthraquinone emodin was present in trace amounts (Panis et al. 2005). Such a chemical composition indicates that raw or incompletely processed fo-ti was used. 

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