Carbon Magnetic Resonance Method

Carbon-13 magnetic resonance (CMR) can play a useful role. Since carbon magnetic resonance deals with analyzing the carbon distribution types, the obvious structural parameter to be determined is the aromaticity, fa Direct determination from the various types of carbon environments is one of the better methods for the determination of aromaticity. Thus, through a combination of proton and carbon magnetic resonance techniques, refinements can be made on the structural parameters, and for the solid-state high-resolution carbon magnetic resonance technique, additional structural parameters can be obtained. 

Mikita, M. A., Steelink, C., and Wershaw, R. L. (1981). Carbon-13 enriched nuclear magnetic resonance method for the determination of hydroxyl functionality in humic substances. Anal. Chem. S3, 1715-1717. 

NMR spectra of (a) a soil humic acid (b) a groundwater fulvic acid (c) a mixture of C-methylated reference compounds (1) pentamethylquercetin (2) glycerol dimethyl ether (3) methyl benzoate (4) methyl pentanoate. Reprinted with permission from Mikita et al., Carbon-13 Enriched Nuclear Magnetic Resonance Method for the Determination of Hydroxyl Functionality in Humic Substances, Anal. Chem. 53, 1715-1717. Copyright 1981, American Chemical Society. 

Davies, J. A., Multinuclear Magnetic Resonance Methods in the Study of Organometallic Compounds, in Hartley, F. R., Patai, S., The Chemistry of the Metal-Carbon Bond, Vol. 1, Wiley, Chichester 1982, pp. 813/918. 

Starting from these methods, as we will see further on, nuclear magnetic resonance (NMR) of carbon has provided an absolute percentage of aromatic, paraffinic, and naphthenic carbons. 

Instmmental methods of analysis provide information about the specific composition and purity of the amines. QuaUtative information about the identity of the product (functional groups present) and quantitative analysis (amount of various components such as nitrile, amide, acid, and deterruination of unsaturation) can be obtained by infrared analysis. Gas chromatography (gc), with a Hquid phase of either Apiezon grease or Carbowax, and high performance Hquid chromatography (hplc), using siHca columns and solvent systems such as isooctane, methyl tert-huty ether, tetrahydrofuran, and methanol, are used for quantitative analysis of fatty amine mixtures. Nuclear magnetic resonance spectroscopy (nmr), both proton ( H) and carbon-13 ( C), which can be used for quaHtative and quantitative analysis, is an important method used to analyze fatty amines (8,81). 

Generally, the most powerful method for stmctural elucidation of steroids is nuclear magnetic resonance (nmr) spectroscopy. There are several classical reviews on the one-dimensional (1-D) proton H-nmr spectroscopy of steroids (267). C-nmr, a technique used to observe individual carbons, is used for stmcture elucidation of steroids. In addition, C-nmr is used for biosynthesis experiments with C-enriched precursors (268). The availability of higher magnetic field instmments coupled with the arrival of 1-D and two-dimensional (2-D) techniques such as DEPT, COSY, NOESY, 2-D J-resolved, HOHAHA, etc, have provided powerful new tools for the stmctural elucidation of complex natural products including steroids (269). 

Other spectroscopic methods such as infrared (ir), and nuclear magnetic resonance (nmr), circular dichroism (cd), and mass spectrometry (ms) are invaluable tools for identification and stmcture elucidation. Nmr spectroscopy allows for geometric assignment of the carbon—carbon double bonds, as well as relative stereochemistry of ring substituents. These spectroscopic methods coupled with traditional chemical derivatization techniques provide the framework by which new carotenoids are identified and characterized (16,17). 

Physical Methods of Examination. Physical methods used to examine coals can be divided into two classes which, in the one case, yield information of a stmctural nature such as the size of the aromatic nuclei, ie, methods such as x-ray diffraction, molar refraction, and calorific value as a function of composition and in the other case indicate the fraction of carbon present in aromatic form, ie, methods such as ir and nuclear magnetic resonance spectroscopies, and density as a function of composition. Some methods used and types of information obtained from them are (41) ... 

Carbon-13 nuclear magnetic resonance spectroscopy is a powerful method for studying brain metabolism. 

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