DEPT NMR

Techniques developed in recent years make it possible to obtain large amounts of information from l3C NMR spectra. For example, DEPT-NMR, for distortionless enhancement by polarization transfer, allows us to determine the number of hydrogens attached to each carbon in a molecule. 

Figure 13.10 DEPT-NMR spectra for 6-methyl-5-hepten-2-ol. Part fa) is an ordinary broadband-decoupled spectrum, which shows signals for all eight carbons. Part [b) is a DEPT-90 spectrum, which shows only signals for the two CH carbons. Part (c) is a DEPT-135 spectrum, which shows positive signals for the two CH and three CH3 carbons and negative signals for the two CH2 carbons.

Most 13C spectra are run on Fourier-transform NMR (FT-NMR) spectrometers using broadband decoupling of proton spins so that each chemically distinct carbon shows a single unsplit resonance line. As with NMR, the chemical shift of each 13C signal provides information about a carbon s chemical environment in the sample. In addition, the number of protons attached to each carbon can be determined using the DEPT-NMR technique. 

Propose structures for molecules that meet the following descriptions. Assume that the kinds of carbons (1°, 2°, 3°, or 4°) have been assigned by DEPT-NMR. 

DEPT-NMR (Section 13.6) An NMR method for distinguishing among signals due to CH3, CH2, CH, and quaternary carbons. That is, the number of hydrogens attached to each carbon can be determined. 

DEPT-NMR spectrum. 6-methyl-5-hepten-2-ol, 451 Detergent, structure of, 1065 Deuterium isotope effect, 386-387 El reaction and, 392 E2 reaction and, 386-387 Dewar benzene. 1201 Dextromethorphan, structure of, 294 Dextrorotatory, 295 Dextrose, structure of. 973 Dialkylamine, pKa of, 852 Diastereomers, 302-303 kinds of, 310-311 Diastereotopic (NMR), 456... 

The 13C NMR spectrum of valproic acid was obtained using a Bruker Avance Instrument operating at 75, 100, and 125 MHz. Standard Bruker Software was used to obtain DEPT spectra. The sample was dissolved in D20 and tetra-methylsilane (TMS) was used as the internal standard. The 13C NMR spectrum of valproic acid is shown in Fig. 10. The DEPT NMR spectra are shown in Figs. 11 and 12. The assignments for the various carbons of valproic acid are presented in Table 4. 

Fig. 16 2-D map of 13C DEPT-MRI spectra recorded along the length of a trickle bed. Separate acquisitions were made for each of the (a) olefinic and (b) aliphatic regions of the spectrum. The data were acquired with the bed operating at steady state for gas and 1-octene flow rates of 32 and 1.0 ml min-1, respectively. The white, horizontal lines indicate the limits of the catalyst packing. Below each 2-D map, the 1-D 13C DEPT NMR spectrum recorded at an axial location just before the reactants reach the catalyst (just above the upper white line) is shown. The peaks at 114 and 139 ppm indicate that only unreacted 1-octene exists within the bed at this location, as expected. 

The structures of the compounds were elucidated by a combination of NMR techniques (lH-, 13C-, and 13C-DEPT NMR) and chemical transformation, enzymatic degradation, and as well as mass spectrometry, which gives information on the saccharide sequence. A more recent approach consists of an extensive use of high-resolution 2D NMR techniques, such as homonuclear and heteronuclear correlated spectroscopy (DQF-COSY, HOHAHA, HSQC, HMBC) and NOE spectroscopy (NOESY, ROESY), which now play the most important role in the structural elucidation of intact glycosides. These techniques are very sensitive and non destructive and allow easy recovery of the intact compounds for subsequent biological testing. 

TABLE 8.5 13C (proton decoupled) and DEPT NMR assignments for zaleplon... 

Determine the structure of the fluorine-containing compound for which the mass, IR, H NMR, l3C/DEPT NMR, and 19F NMR spectra are given. 

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