Optimizing NMR Methods for Structure Elucidation: Characterizing Natural Products and Other Organic Compounds
Chapter 6: One-dimensional Pulse Sequences
Published:26 Sep 2018
Special Collection: 2018 ebook collectionSeries: New Developments in NMR
Optimizing NMR Methods for Structure Elucidation: Characterizing Natural Products and Other Organic Compounds, The Royal Society of Chemistry, 2018, ch. 6, pp. 68-81.
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Depending on the delays between RF pulses and the relative phases and flip angles of these pulses, new spectral information can be obtained with a multiple-pulse sequence that would not be available from a spectrum obtained with a single RF pulse. This is illustrated here with a discussion of different one-dimensional pulse sequences. The first are two sequences designed respectively to measure T1 and T2 relaxation times. As discussed in this and other chapters, knowledge of T1 values is important for the choice of acquisition parameters. The ‘spin-echo’ sequence for measurement of T2 is important, mainly because spin-echo segments are important components of many other pulse sequences. The second types of pulse sequences that are discussed in this chapter are those for 13C spectral editing (i.e., sequences that can distinguish between different peaks in a 13C spectrum based on their number of attached protons). The relative merits of the different sequences are compared and we recommend what we regard as the best choice. The third types of sequences discussed here are those for solvent suppression, i.e., sequences designed to remove solvent peaks or other strong impurities peaks while having a minimal effect on solute peaks. Finally, sequences, called pure shift sequences, that give broadband 1H decoupling in 1H spectra and in some 1H-detected 2D sequences are discussed.