Physical Methods for Structural Elucidation

Physical Methods for Structural Elucidation I. Mass Spectrometry 

Mass spectrometry has proved to be a useful complement to other methods for elucidating the structure of cyclic acetals. The reader is referred to several excellent reviews on the mass spectrometry of carbohydrates that have appeared within the time span covered by this article.65a 65 1,66 Mass spectrometry is a valuable aid for distinguishing pyranose from furanose structures, and monoacetals from diacetals. It may also facilitate the assignment of ring location. However, it is generally insensitive to configurational differences. 

Isopropylidene acetals are by far the most well-studied derivatives. The fragmentation patterns of isopropylidene acetals of pentoses and hexoses have been delineated by Dejongh and Biemann.67 

The mass spectra of the diisopropylidenealdofuranoses differ considerably from those of the corresponding acetals of the pyranoses. The most characteristic process is the scission of the C-4-C-5 bond, resulting in two typical fragments having mle 101 and 159, as shown in 19. The corresponding fragments A, B, C, and D are lessened in in- 

Chizhov and coworkers69 established an important fragmentation-pattern ( h-rupture ) that accounts for the ions mle 101, 129, and 159 in the mass spectra of di-O-isopropylidene-pentoses (20) and -hexoses. 

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In addition to the Annual Reports on NMR Spectroscopy monograph reviewing H-NMR and, 3C-NMR spectroscopy of alkaloids in three volumes (305), several books and reviews appeared concerning the 13C-NMR spectroscopy of naturally occurring substances (306-308). Therefore we would like to present only a limited number of examples of the exceptional applicability of these physical methods for structure elucidation and conformational analysis of complex molecules. 

PHYSICAL METHODS FOR STRUCTURAL ELUCIDATION OF OLIGOMERIC ELLAGITANNINS... 

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