Structure Elucidation - Natural Products Chemistry: Sources, Separations, and Structures - page 31

FIGURE 3.10 X-ray crystallographic structure of the parnafungin derivative. (From Parish,
S. K. et al., 2008, J Am Chem Soc 130(22):7060-7066. With permission from the American
Chemical Society.)
QUESTIONS
1. What are the main spectroscopic techniques used for structure
determination?
2. Which nuclei lend themselves to NMR?
3. Why is the methylene in ethanol (CH 3 CH 2 OH) observed as a quartet in the
H- NMR spectrum?
4. Why is the quartet seen as a ratio of 1:3:3:1?
5. What do you understand about the term 500MHz H-NMR spectrum ?
6. What other sized instruments are available? What are the benefits of each one?
7. Why is TMS used as an internal standard for running NMR spectra?
8. In mass spectrometry, what do you understand about the terms positive ion
mode and negative ion mode ?
9. In X-ray crystallography the compound of interest is often derivatized with
the addition of a group containing a “heavy” atom. Give an example and
explain the reason.
FURTHER READING
1. C. A. Parish, S. K. Smith, K. Calati, D. Zink, K. Wilson, T. Roemer, B. Jiang, et al.
2008. Isolation and structure elucidation of parnafungins, antifungal natural products
that inhibit mRNA polyadenylation. J Am Chem Soc 130(22):7060-7066.