Optimizing NMR Methods for Structure Elucidation: Characterizing Natural Products and Other Organic Compounds
Chapter 8: Two-dimensional Homonuclear Spectroscopy
Published:26 Sep 2018
Special Collection: 2018 ebook collectionSeries: New Developments in NMR
2018. "Two-dimensional Homonuclear Spectroscopy", Optimizing NMR Methods for Structure Elucidation: Characterizing Natural Products and Other Organic Compounds, Darcy C Burns, William F Reynolds
Download citation file:
The relative merits of three different kinds of COSY spectra (COSY-90, COSY-45 an DQ-COSY) are compared and the importance of obtaining these spectra with good data point resolution is stressed. We conclude that COSY-45 is the best choice for structure elucidation while DQ-COSY, in combination with a resolution-enhanced 1H spectrum in structure elucidation is discussed, with particular emphasis of the value of selective 1D-TOCSY spectra with arrayed mixing times for this purpose. The relative merits of NOESY and ROESY for nuclear Overhauser enhancements (nOe) are discussed, with emphasis of the importance of molecular weight when choosing the appropriate sequence for a molecule. The use of selective 1D NOESY measurements for accurate inter-proton distance measurements is discussed, while the older nOe difference method is recommended in place of 1D NOESY when only qualitative nOe information is needed. Problems caused by COSY artifacts when evaluating nOE data are discussed and the value of an EXSY spectrum for investigating molecular exchange is highlighted. The chapter ends with specific recommendations for optimum acquisition parameters and processing methods for each sequence, followed by a summary of key recommendations made in the chapter.