Configuration proton magnetic resonance spectroscopy

In favorable cases, cyclization reactions may be useful in estab-hshing configurations, but these methods may also be complicated by isomerizations. It is clear that other approaches are necessary to resolve this structural question. This has been accomplished recently for the isomers of a related system (55) using proton magnetic resonance spectroscopy. 

Proton magnetic resonance spectroscopy was of no avail in the study of complex formation of Me2SnCl2 with pyridine in solution since insoluble species are formed with any ratio of reactants. An III spectrum of the Me2SnCl2-7-picoline complex contains (61) a strong singlet for cas(Sn—C), at 560 cm-1, and a broad Sn—Cl multiplet at 233 cm-1, suggesting the Ilia structure. The J( H—C—nl Sn) value of 102.0 Hz found for the solution in CHCh (145), and corrected for the possibility of dissociation, may confirm that the configuration is retained in solution. 

The relative, specific optical rotations of each pair of anomers support the configurations assigned by proton magnetic resonance spectroscopy. 

Treatment of cw-humulinic acid with alkali caused it to revert to the trans form the equilibrium mixture consists of over 90% of rra/i -humulinic acid. Oxidation of n>humulinic acid with bismuth oxide also gave dehydrohumulinic acid [79]. This result suggested that the two humulinic acids were epimeric at C-4 and this was confirmed by proton magnetic resonance spectroscopy [79]. Thus in rr AW-humulinic acid (77 or 80 R = H) the C-4 hydroxy group and the C-5 isopentenyl chain have the trans configuration and lie on opposite sides of the planar cyclopentenone ring. In cw-humulinic acid (79 or 81 R = H) both bulky substituents lie on the same side of the ring. All these compounds exist as mixtures of tautomers. 

Resonance spectroscopies have an important role in determining electronic configurations and protein conformations. High resolution proton magnetic resonance may provide information on conformations in solu-... 

Proton magnetic resonance (p.m.r.) spectroscopy is now firmly established as the most widely used technique for the structural, configurational, and conformational analysis of carbohydrates and their derivatives. Much of the earlier work on the application of... 

One other pyridine alkaloid has been detected in dendrobatid frogs. The structure of this minor alkaloid, noranabasamine (XIII), was established by proton and carbon-13 magnetic resonance spectroscopy (14). The ultraviolet spectrum was as follows X ,ax (CH3OH) 244 nm, e 11,000, 275 nm, e 10,000. The optical rotation, [a]o, was -14.4° (CH3OH). Anabasamine, a plant alkaloid, also is levorotatory, but it is unknown whether noranabasamine, now given a code number 239J, has the same 2S configuration. 

Since about 1960 nuclear magnetic resonance (NMR) spectroscopy has become an important tool for the study of chain configuration, sequence distribution and microstructure of polymers. Its use started from early broad-line studies of the one-set of molecular motion in solid polymers and passed through the solution studies of proton NMR, to the application of the more difficult but more powerful carbon-13 NMR methods to both liquids and solids. 

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