Distortionless enhanced polarization

Of the multitude of ID 13C NMR experiments that can be performed, the two most common experiments are a simple broadband proton-decoupled 13C reference spectrum, and a distortionless enhancement polarization transfer (DEPT) sequence of experiments [29]. The latter, through addition and subtraction of data subsets, allows the presentation of the data as a series of edited experiments containing only methine, methylene and methyl resonances as separate subspectra. Quaternary carbons are excluded in the DEPT experiment and can only be observed in the 13C reference spectrum or by using another editing sequence such as APT [30]. The individual DEPT subspectra for CH, CH2 and CH3 resonances of santonin (4) are presented in Fig. 10.9. 

The carbon and DEPT (distortionless enhanced polarization transfer) spectra are shown in Figure 10. The HETCOR (heteronuclear two-dimensional proton-carbon correlation) spectrum is shown in Figure 11. The carbon assignments are listed in Table 5. Long-range HETCOR experiments were used to make the assignments for the thiophene carbons. 

DEPT (Distortionless Enhanced Polarization Transfer) is a more recent technique that provides the same information as off-resonance decoupling. DEPT is easier to run on modem, computer-controlled Fourier transform spectrometers. DEPT gives better sensitivity, and it avoids overlapping multiplets because all the peaks remain decoupled singlets. 

Distortionless Enhanced Polarization Transfer) A method of running several 13C experiments with different pulse sequences so that the carbon atoms appear differently depending on whether they are bonded to 0, 1, 2, or 3 protons, (p. 607)... 

The DEPT experiment, or distortionless enhanced polarization transfer, is a carbon selectivity experiment.29-35 Based on the pulse length selected, one... 

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... 

The distortionless enhanced polarization transfer (DEPT) experiment is a carbon selectivity experiment.HO-116 Depending on the pulse length selected, one can selectively observe different types of carbon entities. We recommend setting the DEPT proton pulse length to 135°. In this case, quaternary carbons are suppressed, methylenes are inverted, and methine and methyl carbons... 

DEPT NMR spectta (Section 9.1 ID) Distortionless enhanced polarization transfer (DEPT) C NMR spectra indicate how many hydrogen atoms are bonded to a given carbon atom. 

Distortionless enhanced polarization transfer (DEPT) spectra... 

The DEPT experiment, or distortionless enhanced polarization transfer, is a carbon selectivity experiment. ° ° ° Depending on the pulse length selected, one can selectively observe different types of carbon entities. We recommend setting the DEPT proton pulse length to 135°. In this case, quarternary carbons are suppressed, methylenes are inverted, and methine and methyl carbons appear upright. Methines and methyls are distinguished based on chemical shift and 2D proton correlations. Methines usually appear downfield of methyls. Alternatively, if time permits, the entire series of DEPT experiments can be performed to conclusively distinguish methine from methyl resonances. One second is a reasonable default value for the recycle time. The spectrum should be set to capture the resonances of interest with 32-64 K data points and four dummy scans. While this is an easily interpreted data set, the multiplicity edited HSQC provides much more robust information, both multiplicity as well and the one-... 

The DEPT (distortionless enhanced polarization transfer) pulse sequence is probably one of the most widely used of all NMR experiments. It produces subspectra edited according to the number of protons bonded to each The DEPT pulse... 

The zero sum of intensities in a multiplet in these differential polarization transfer experiments means that any decoupling that causes all the lines to coalesce results in exact cancellation of intensities. Several methods have been devised to avoid this problem when decoupling is required. One is pulse-interrupted precession,which results in a net polarization transfer, as does the insertion of a properly chosen delay period in the INEPT sequence (as in Figure 12) so that all members of a multiplet appear positively enhanced, i.e., INEPT with refocusing (INEPTR). The DEPT (Distortionless Enhancement Polarization Transfer) sequence gives undistorted relative intensities of the multiplet components. 

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