DEPT Technique

DEPT technique, 725 -6 dialkyl peroxide determination, 708 Eourier transform, 695 hydroperoxides... 

Infrared spectra of the unfilled and filled copolymers were measured using a Perkin-Elmer model 1700 FTIR spectrometer. The 13C CP/MAS NMR measurements were conducted on a Bruker 300 instrument operating at 75.51 MHz. The samples were rotated with a spectra width of 40.0 Hz, the CP time was 5 ms. l3C lI distortionless enhancement by polarization transfer (DEPT) technique was applied for analysis of monomers. The process was performed at 75.51 MHz, rotated with a spectral width of 0.75 Hz and a CP time of 15 ms. Atomic force microscopy measurements were carried out using a Nanoscope Ilia controlled Dimension 3000 AFM (Digital Instrument, Santa Barbara, CA). 

Different types of protons and carbons in alkanes tend to absorb at similar chemical shifts, making structure determination difficult. Explain how the 13C NMR spectrum, including the DEPT technique, would allow you to distinguish among the following four isomers. 

Up-to-Date Treatment In addition to the classical reactions, this book covers many techniques and reactions that have more recently gained wide use among practicing chemists. Molecular-orbital theory is included early and used to explain electronic effects in conjugated and aromatic systems, pericyclic reactions, and ultraviolet spectroscopy. Carbon-13 NMR spectroscopy is treated as the routine tool it has become in most research laboratories, and the DEPT technique is included in this edition. Many of the newer... 

Polarization Transfer NMR Spectroscopy for Silicon-29 The INEPT and DEPT Techniques,... 

The J-modulated spin-echo technique " and the DEPT technique " are pulse sequences, which transform the information of the CH signal multiplicity and of spin-spin coupling into phase relationships (positive and negative amplitudes) of the C signals in the proton decoupled C NMR spectra. The DEPT technique benefits from a polarisation transfer which increases the sensitivity by up to a factor of 4. For... 

INEPT and DEPT techniques have also been applied to nuclei other than 29Si. See refs. 2-5. 

Although there are differences (noted above) between the INEPT and DEPT techniques, the fundamental polarization transfer mechanism is the same (3,4,13). Thus, for simplicity, INEPT will be used to demonstrate the use of polarization transfer in 29Si-NMR, except in cases where a comparison with DEPT would be advantageous. 

There are two cases in which the DEPT technique offers advantages over INEPT. First, in coupled spectra, DEPT gives normal multiplet phases and intensities, which may aid interpretation and are certainly more familiar in appearance than those obtained from INEPT. In addition, coupled DEPT spectra tend to be better resolved than the corresponding INEPT spectra, especially for complex spin systems (see Fig. 3). This is probably a consequence of DEPTs lesser J dependence compared to INEPT. Second, for samples in which large J variations are present or suspected, DEPT is the method of choice because it is less likely to suppress signals than INEPT (see Fig. 5). 

Despite its utility, off-resonance decoupling is now considered an old-fashioned technique. It has been replaced by more modem methods, the most important of which is Distortionless Enhancement by Polarization Transfer, better know as DEPT. The DEPT technique requires an FT-pulsed spectrometer. It is more complicated than off-resonance decoupling and it requires a computer, but it gives the same information more reliably and more clearly. Chapter 10 will discuss the DEPT... 

In the DEPT technique, the sample is irradiated with a complex sequence of pulses in both the and channels. The result of these pulse sequences is that the C signals for the carbon atoms in the molecule wiU exhibit different phases, depending on the number of hydrogens attached to each carbon. Each type of carbon will behave slightly differently, depending on the duration of the complex pulses. These differences can be detected, and spectra produced in each experiment can be plotted. 

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