Optimizing NMR Methods for Structure Elucidation: Characterizing Natural Products and Other Organic Compounds
Chapter 5: Acquiring 1H and 13C Spectra
Published:26 Sep 2018
Special Collection: 2018 ebook collectionSeries: New Developments in NMR
2018. "Acquiring 1H and 13C Spectra", Optimizing NMR Methods for Structure Elucidation: Characterizing Natural Products and Other Organic Compounds, Darcy C Burns, William F Reynolds
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This chapter begins with tabulation of average 1H and 13C relaxation times for a series of typical organic molecules with molecular weights between 150 and 450 Daltons. These values are essential for choosing acquisition parameters (particularly recycle times) for both 1D and 2D spectral acquisitions. Next, recommendations for solvent choice and sample preparation are provided, followed by a discussion of magnetic field shimming. This is followed by specific recommendations for acquiring and processing semi-quantitative 1H and 13C spectra. The latter recommendations differ from commonly used values by stressing the importance of high data point resolution, combined with smaller than usual line-broadening parameters to enhance the signal/noise of non-protonated carbons. In addition, specific recommendations for reporting 1H and 13C spectral data are provided. The last section discusses acquisition of quantitative 1H data. Again, specific recommendations for acquisition parameters are provided, followed by a discussion of the relative merits of internal versus external referencing for acquiring quantitative data. Finally, the use of spectral fitting programs is recommended in place of peak integration and likely sources of errors in quantitative NMR are discussed. The chapter ends with a summary of the specific recommendations included in the chapter.