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- W255205019 abstract "Basic Parameters and Conditions for Recording PMR Spectra. The interpretation of PMR spectra is based on three parameters characterizing the absorption of the energy of a radiofrequency field by hydrogen nuclei present in a constant magnetic field: i) the chemical shift of the signal measured in parts per million (ppm) from the intensity of the external magnetic field and determining the position of the absorption signal in the spectrum; 2) the multiplicity of the signal and the coupling constant J, measured in hertz; 3) the integral intensity or area of the absorption signal -- S. The chemical shift of the signal of a proton depends on the nature of the closest substituents and chemical bonds. The multiplicity of the signal the number of components into which the absorption signal is split -- is determined by the number of adjacent protons, and the size of the coupling constant -- the distance between the components of the signal -- depends on the geometric arrangement of the interacting protons and on the electronegativit ies of the substituents on the neighboring carbon atoms. The areas of the absorption signals are proportional to the numbers of protons responsible for these signals. PMR spectra are recorded for mobile liquids or for solutions of solids in certain solvents. The choice of solvent is determined by the solubility of the substance to be analyzed, which, for measurements in modern pulsed spectrometers, may amount to fractions of apercent at molecular weights of up to 500. The PMR signals of the solvent must not overlap the region of the signals of the substances being analyzed. For the majority of organic substances the absorption signals of the protons of various groups are recorded in the range of ~ of from 0.7 to i0 ppmo In order to decrease the intensity of the signals of the solvents, which in some cases exceeds the intensities of the signals of the substances being analyzed hundreds oftimes, aprotic or deuterated solvents with isotropic enrichments by deuterium of above 97% are used. The chemical shifts of the signals of the residual protons of the deuterated solvents used most frequently are given in Table i. To measure PMR chemical shifts, standard substances added in small amounts (less than i%) to the compounds to be analyzed are used (internal standards). For solutions in organic solvents tetramethylsilane (TMS) is used, its singlet absorption signal being taken as~the zero in the calculation of chemical shifts (6 = 0.0 ppm). In aqueous media, sodium 2,2" @default.
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- W255205019 date "1983-01-01" @default.
- W255205019 modified "2023-09-27" @default.
- W255205019 title "INVESTIGATION OF THE STRUCTURE OF CHEMICAL COMPOUNDS, METHODS OF ANALYSIS, AND QUALITY CONTROL USE OF PMR SPECTROSCOPY IN THE ANALYSIS OF DRUGS (REVIEW)" @default.
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