Distortionless Enhancement by Polarisation Transfer

DEPT Distortionless enhancement by polarisation transfer, differentiation between CH, CH2 and CH by positive CH, CH3) or negative CH signal amplitudes, using improved sensitivity of polarisation transfer... 

The 13C chemical shifts were assigned in more detail for monosulfidic and polysulfidic crosslinks occurring in the accelerated sulfur vulcanisation of NR [18]. The NR was cured with a pure thiuram formulation (TMTD alone) in order to predominantly prepare monosulfidic bridges in the network. The distortionless enhancement by polarisation transfer (DEPT) experiments, in which the carbons with different level of protonation can be distinguished [22-24], were performed for the NR cured with extended levels of sulfur. Based on the DEPT results and previously reported model compound results [20], the chemical shifts of the resonances occurring in the spectra were assigned. 

The sensitivity of is inconveniently low, and in the conventional H-decoupled spectrum the excitation of the proton resonances increases the strength of the signal in addition to simplifying it. However, rather than simply applying rf power to the protons, a series of pulses to both protons and carbons results in Distortionless Enhancement by Polarisation Transfer (DEPT) and gives one-dimensional spectra with usefully higher sensitivity than from proton decoupling. Additionally, the one-dimensional spectrum... 

The DEPT experiment [33] (Distortionless Enhancement by Polarisation Transfer) is the most widely used polarisation transfer editing experiment in carbon-13 spectroscopy, although its application is certainly not limited to the proton-carbon combination. It enables the complete determination of all carbon multiplicities, as does the refocused INEPT discussed above, but has a number of distinct advantages. One of these is that it directly produces multiplet patterns in proton-coupled carbon spectra that match those obtained from direct observation, meaning methylene carbons display the familiar 1 2 1 and methyl carbons the 1 3 3 1 intensity patterns this is the origin of the term distortionless . However, for most applications proton decoupling is applied during acquisition and multiplet structure is of no consequence, so the benefits of DEPT must lie elsewhere. 

DEPT Distortionless enhancement by polarisation transfer (spectrum editing) 4.4.3... 

NMR is the tool most widely used to identify the structure of triterpenes. Different one-dimension and two-dimension techniques are usually used to study the structures of new compounds. Correlation via H-H coupling with square symmetry ( H- H COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC), distortionless enhancement by polarisation transfer (DEPT), incredible natural abundance double quantum transfer experiment (INADEQUATE) and nuclear Overhauser effect spectroscopy (NOESY) allow us to examine the proton and carbon chemical shift, carbon types, coupling constants, carbon-carbon and proton-carbon connectivities, and establish the relative stereochemistry of the chiral centres. 

This method works well in a molecule which has well spaced peaks, but is less successful in larger molecules. An alternative method is to measure what it known as a DEPT spectrum (Distortionless Enhancement by Polarisation Transfer). The DEPT spectrum plots the CH3, CH2 and CH peaks separately. It does not record carbon atoms which do not have a hydrogen atom attached, so we need a decoupled spectrum as well as a DEPT spectrum. The spectra for butan-l-ol are shown in Figure 5.2. 

A readily available alternative that is particularly suitable for (although not restricted to) proton calibration in H-X systems is the distortionless enhancement by polarisation transfer (DEPT) sequence (Chapter 4). This improves observation sensitivity by making use of polarisation transfer from to X and is dependent on the faster relaxing protons for repetition... 

DEPTQ Distortionless enhancement by polarisation transfer retaining quaternary centres 4.4.4... 

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