Distortionless enhancement example

Techniques developed in recent years make it possible to obtain large amounts of information from l3C NMR spectra. For example, DEPT-NMR, for distortionless enhancement by polarization transfer, allows us to determine the number of hydrogens attached to each carbon in a molecule. 

HSQC) or heteronuclear multiple quantum correlation (HMQC). The combined experiments such as 2D HSQC(HMQC)-TOCSY experiments are powerful tools for the assignment of the 13C and 11 resonances belonging to the same sugar residue providing enhanced dispersion of TOCSY correlations in the carbon dimension. More recendy, different carbon multiplicity editing methods, for example, DEPT (distortionless enhanced polarization transfer)-HMQC and E-HSQC, have been developed to reduce the complexity of proton-carbon correlation spectra and to enhance the resolution by narrowing the applied spectral window.11... 

A number of papers have looked at the development of relationships between base stock composition as measured by NMR and either physi-cal/chemical properties or their performance.22 27 Most of this work has been focused on group II and III base stocks, with less or little attention paid to solvent extracted ones. These have all relied on various techniques to simplify the spectra and the assignments of peaks and make peak integration more reliable. These have many acronyms,23 for example, GASPE (gates spin echo), PCSE (proton coupled spin echo), INEPT (insensitive nuclei enhancement by polarization transfer), DEPT (distortionless enhancement by polarization), QUAT (quaternary-only carbon spectra), 2D COSY (two-dimensional homo-nuclear spectroscopy), and HETCOR (heteronuclear shift correlated spectroscopy)]. Table 4.10 provides an example of some of the chemical shift data generated26 and employed in this type of work, and Adhvaryu et al.25 were able to develop the correlations between base stock properties and carbon types in Table 4.11, whose main features correspond to intuition (e.g., the values of API and aniline points are both decreased by aromatic carbon and increased by the... 

Just as important as these developments in magnet design has been the introduction of pulsed Fourier transform methods, for these permit the performance of new types of experiment by the computerised systems that control the production, acquisition and processing of the experimental data. New pulse sequences increasingly made available by instrument manufacturers within their software suites permit the routine performance of these new experiments an early example is the distortionless enhancement polarisation transfer, or DEPT, experiment to identify the number of protons attached to a carbon by controlling the final... 

The other commonly seen spectral editing techniques used in carbon NMR involve the transfer of polarization from protons to carbons in particular ways. A good example of this type of experiment is the so-called DEPT (distortionless enhancement by polarization transfer) sequence (Figure 5). By careful choice of experimental parameters, one can obtain spectra that represent only the quaternary, only the methines, only the methylenes and only the methyl groups in the sample. This is done in this case by use of the sequence shown in Figure 5. Four spectra are obtained with <5 =7t/4, jtH, and 3 7r/4 in the sequence... 

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