Structure Deduction from Multiple Spectra

As previously discussed, different types of spectra have different data structure and interpretation rules. To deduce the structure from these multiple spectra, we need to choose one of the spectra as the base spectrum and then start our analysis. Typically, the base spectrum should have an explicit correlation between substructure and subspectra. For instance, the NMR spectrum provides explicit structure-spectrum relations. We now select the one-dimensional NMR speetrum as the base spectrum to show one of the structure elucidation strategies. Other spectra, such as infrared or two-dimensional NMR spectra, are used as constraints to reduce the search space. This strategy is outlined in Fig. 19. 

In this scheme, the most computationally time-consuming procedure is the connection of the atoms or substructures to generate structure candidates. We illustrate this scheme via elucidation of the structure of gib-berellic acid (GBA). The molecular formula of gibberellic acid was determined as C19H22O5 from mass spectroscopy. By using a C distortionless 

FIGURE 19 One of the general schemes for structure elucidation from multiple spectra. 

By adding C, H-COSY spectral peaks. Table VI becomes Table VII. Also, more entries are filled. The H, C atomic connections are generated, although they are far from complete. Combined with H, H-COSY peaks. Table VII becomes Table VIII. More C,C atomic connections are generated by COSY. In the column Bond Adjacency, the bond information is recorded. For example, at row 4, column 6, 5/2,9/1 means that the 

TABLE VI Deduction of the Gibberellic Acid Structure Generated from Mass Spectroscopy and DEPT 

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