Pulse sequence , DEPT spectroscopy

A very useful pulse sequence in spectroscopy is employed in the experiment called Distortionless Enhancement by Polarization Transfer, better known as DEPT. The DEPT method has become one of the most important techniques available to the NMR spectroscopist for determining the number of hydrogens attached to a given carbon atom. The pulse sequence involves a complex program of pulses and delay times in both the and ehannels. The result of this pulse sequenee is that carbon atoms with one, two, and three attached hydrogens exhibit different phases as they are recorded. The phases of these hydrogens will also depend on the duration of the delays that are programmed into the pulse sequence. In one experiment, called a DEPT-45, only carbon atoms that... 

The INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) experiment [6, 7] was the first broadband pulsed experiment for polarization transfer between heteronuclei, and has been extensively used for sensitivity enhancement and for spectral editing. For spectral editing purposes in carbon-13 NMR, more recent experiments such as DEPT, SEMUT [8] and their various enhancements [9] are usually preferable, but because of its brevity and simplicity INEPT remains the method of choice for many applications in sensitivity enhancement, and as a building block in complex pulse sequences with multiple polarization transfer steps. The potential utility of INEPT in inverse mode experiments, in which polarization is transferred from a low magnetogyric ratio nucleus to protons, was recognized quite early [10]. The principal advantage of polarization transfer over methods such as heteronuclear spin echo difference spectroscopy is the scope it offers for presaturation of the unwanted proton signals, which allows clean spec-... 

The imaging of conversion within the fixed bed was achieved by using a distortionless enhancement by polarization transfer (DEPT) spectroscopy pulse sequence integrated into an imaging sequence, as shown in Fig. 44. In theory, a signal enhancement of up to a factor of 4 (/hZ/c 7i is the gyromagnetic ratio of nucleus i) can be achieved with DEPT. In this dual resonance experiment, initial excitation is on the H channel. Consequently, the repetition time for the DEPT experiment is constrained by Tih (< T lc) where Tn is the Ty relaxation time of... 

Another milestone in Ge NMR was made by the introduction of high field instruments coupled with the advancement of software technology. Use of high field instruments is particularly advantageous for low frequency nuclei such as Ge. Observation of the Ge resonance of larger and less symmetric compounds became possible in certain cases. Use of advanced software has also widened the scope of Ge NMR spectroscopy. Thus, INEPT and DEPT pulse sequences achieved several fold signal enhancement (and hence corresponding reduction in machine time). Application of 2D techniques to Ge NMR spectroscopy has also been reported. 

Two new polarization transfer techniques have recently been reported INEPT (2) and DEPT (3,4). These pulse sequences lack the limitations of previous polarization transfer methods, and allow the routine collection of 29Si-NMR data. The principal virtues of both the INEPT and DEPT pulse sequences are that the polarization transfer enhancements are substantial (five- to ninefold) (12) and relatively nonselective and that they can easily be used by chemists familiar with normal FT-NMR spectroscopy on available commercial multinuclear FT-NMR instruments. 

Fig. 6.19. Pulse sequence for DEPT spectroscopy. The third H pulse is variable with 9 = 45°, 90° and 135°, The delay time t is set to (2ycH) - (Reproduced from Ref. [52]. 1986 American Chemical Society.)...

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