Nuclear magnetic resonance deducing chemical structure

Virtually, all students of chemistry, biochemistry, pharmacy and related subjects learn how to deduce molecular structures from nuclear magnetic resonance (NMR) spectra. Undergraduate examinations routinely set problems using NMR spectra, and masters and doctoral theses describing novel synthetic or natural products provide many examples of how powerful NMR has become in structure elucidation. Existing texts on NMR spectroscopy generally deal with the physical background of the newer and older techniques as well as the relationships between NMR parameters and chemical structures. Very few, however, convey the know-how of structure... 

Since the 1950s, nuclear magnetic resonance (NMR) has found wide application in the solution of chemical problems, including numerous applications in the field of Grignard reagents. Chemical shift and spin-spin-coupling data enable the chemist to determine the location of magnetically active nuclei in a molecule of interest, and to obtain preliminary structural information often not readily deducible by other methods of spectroscopy. 

The experimental results obtained by the nuclear magnetic resonance (NMR) method can be used to determine the nature of the chemical bonding and, particularly, the susceptibility and the carrier density. Nuclear magnetic resonance can be used to deduce information on the structure of a substance from the resonance line width and profile, from the spin-lattice relaxation, and from the shift of the resonance frequency. We shall consider some results obtained from the shift of the NMR line. 

The structure of aCA was deduced by Holzapfel (1968) on the basis of chemical and physicochemical investigations. The compound was originally formulated as the enol tautomer (5) of the acyltetramic acid (4). A recent nuclear magnetic resonance (NMR) study (Steyn and Wessels, 1978) of cyclopiazonic acid indicated that it exists as a mixture of three tautomers. 

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