DEPT routine

In the DEPT routine, a second transmitter excites H, and this affects the appearance of the spectrum. A typical DEPT experiment is illustrated for the case of 1-phenyl-1-pentanone in Figure 13.23. In addition to the normal spectrum shown in Fig-... 

Chaimelling phenomena were studied before Rutherford backscattering was developed as a routine analytical tool. Chaimelling phenomena are also important in ion implantation, where the incident ions can be steered along the lattice planes and rows. Channelling leads to a deep penetration of the incident ions to deptlis below that found in the nonnal, near Gaussian, depth distributions characterized by non-chaimelled energetic ions. Even today, implanted chaimelled... 

You may be told that your NMR laboratory does not routinely use APT spectra but provides DEPT spectra (Distortionless Enhancement by Polarization Transfer) instead. This is no problem, as DEPT spectra also provide you with the information you need just go back and read what we have said about the relative merits of APT and DEPT. 

The DEPT sequence (distortion enhancement by polarization transfer) has developed into the preferred procedure for determining the number of protons directly attached to the individual 13C nucleus. The DEPT experiment can be done in a reasonable time and on small samples in fact it is several times more sensitive than the usual 13C procedure. DEPT is now routine in many laboratories and is widely used in the Student Exercises in this textbook. The novel feature in the DEPT sequence is a variable proton pulse angle 9 (see Figure 4.11) that is set at 90° for one subspectrum, and 135° for the other separate experiment. 

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... 

The spectra shown in this problem provide relatively routine practice. In the DEPT spectra, the methine and methyl carbons give positive peaks and methylene carbons negative peaks at the top. Only methine carbons are in the middle, and a full spectrum of all carbons is at the bottom. The H spectra were recorded at 300 MHz and the spectra at 75 MHz. The spectra are as follows ... 

The use of NMR for the compositional analysis of crude oils and fractionated products is routine in industrial production. Common analyses include the determination of saturated and aromatic hydrocarbon content, average structural parameters such as the percentages of n-paraffins, / 6>-paraffins, cyclo-paraffins, mono-, di-, and poly aromatics. These data are used for the development of correlations between the compositions and their characteristics.Spectral editing such as DEPT is routinely used for the unambiguous assignments of resonances in complex mixtures, and recent trends indicate the utility of 2D-correlation techniques for such purpose. " In addition, NMR is used to determine additive constituents... 

Because of very complex terrain the application of simple dispersion models is very limited in Slovenia. Traffic pollution and the high level of surface ozone are the main current air pollution problems in the country. No official standard model for regulatory purposes has been accepted in Slovenia up to present. The US EPA model ISC3 is used for routine dispersion calculations from point sources. Some other imported models were tested in Slovenia but only on research basis. A neural network forecasting model was developed for the Sostanj thermal power plant. No urban air pollution studies are reported from Slovenia. Air pollution modelling is performed at the Jozef Stefan Institute, Dept, of Environmental Sciences, Ljubljana, Slovenia (US, 2005), AMES d.o.o. and the Hydrometeorological service. 

Hull, T.E., Enright, W.H. and Jackson, K.P., 1972, User s guide for DVERK a routine for solving non-stiff ODE TR//JO0, Dept. Comp, Sci., Univ. of Toronto. 

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. 

The INEPT and DEPT pulse sequences shown in Fig. 1 (IS, 14) are all multinuclear pulse sequences in which proton and/or silicon pulses are separated by free precession periods. However, INEPT and DEPT differ in both the number and duration of precession periods. In the INEPT pulse sequences, there are two precession periods of duration t, and one of duration A [a refocusing pulse (15) bisects the A period]. Both t and A are parameters set by the user to optimize enhancements, although t is routinely set to a constant (4J) 1 (where J is the H-29Si coupling constant). The A parameter can be set according to Eq. (5) (Section IV,A) to obtain optimal enhancement, or may be set to selectively invert or suppress specific silicon resonances as shown by Figs. 8-10 (Section III,D). 

The presentation of subspectra can be condensed to two lines as shown in Figure 5.6 and in Chapter 6. One line (B subspectrum) shows peaks CH3 and CH up, and CH2 down. The other line (A subspectrum) shows the CH peaks up. Quaternary carbon atoms are not recorded in a subspectrum since there is no attached proton, but of course the main (conventional 13C) spectrum does show these peaks. In many laboratories, a DEPT spectrum is considered part of a routine 13C spectrum. 

A comparison of DEPT-135 with both the original and enhanced DEPTQ is made in Pig. 4.36 demonstrating the retention of quaternary centres and the improved performance achievable with the enhanced version. This method would now appear to be the optimal approach to spectrum editing with retention of all carbon centres and is attractive as a routine carbon-13 screening tool for the organic laboratory. The use of frequency-swept (adiabatic) 180° pulses is equally valid for the standard DEPT sequence, or indeed any using 180° pulses, and should also provide enhanced performance when large carbon bandwidths become problematic see Chapter 10 for more information on these. 

Nuclear Magnetic Resonance Spectroscopy. Like IR spectroscopy, NMR spectroscopy requires little sample preparation, and provides extremely detailed information on the composition of many resins. The only limitation is that the sample must be soluble in a deuterated solvent (e.g., deuterated chloroform, tetrahydro-furan, dimethylformamide). Commercial pulse Fourier transform NMR spectrometers with superconducting magnets (field strength 4-14 Tesla) allow routine measurement of high-resolution H- and C-NMR spectra. Two-dimensional NMR techniques and other multipulse techniques (e.g., distortionless enhancement of polarization transfer, DEPT) can also be used [10.16]. These methods are employed to analyze complicated structures. C-NMR spectroscopy is particularly suitable for the qualitative analysis of individual resins in binders, quantiative evaluations are more readily obtained by H-NMR spectroscopy. Comprehensive information on NMR measurements and the assignment of the resonance lines are given in the literature, e.g., for branched polyesters [10.17], alkyd resins [10.18], polyacrylates [10.19], polyurethane elastomers [10.20], fatty acids [10.21], cycloaliphatic diisocyanates [10.22], and epoxy resins [10.23]. 

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