Decoupled spectrum

Conditions CDCI3, 25 °C, 100 MHz ( C), 400 MHz H). (a-e) C NMR spectra (a,b) //broadband decoupled spectra (c,d) NOE enhanced coupled spectra (gated decoupling) with expansion (e) of the multiplets in the sp shift range (f) //NMR spectrum with expanded multiplets. 

How can spectral editing in INEPT be used to generate separate spectra for CH, CH2, and CH3 groups, and how is it superior to the traditional off-resonance decoupled spectra ... 

Figure 15 shows the normal broad-band decoupled and gated decoupled spectra of compound 1 in the latter we can see the multiplets arising from C-H coupling (across one or more bonds) and C-P coupling. The rules for the number of lines in a multiplet and their intensities are the same as for protons, since 13C and 31P are both spin-Vi nuclei. 

MHz, solvent CDC13 13C broad band decoupled and 13C gated decoupled spectra Assign all signals and calculate and tabulate coupling constants nJ(P-C) and11J(C-H)... 

Compounds 1 and 2 were identified by FTIR and 13C-NMR. The 13C proton decoupled spectra for 1 and 2 are dominated by signals ranging from 62 to 195 ppm. The 13C chemical shift assignments were made based on comparisons with 4,4 -(hexafluoroisopropylidene)diphenol and from calculations based on substituted benzenes and naphthalenes.15 The 13C-NMR spectrum clearly showed that the Friedel-Crafts acylation of 1 by 4-fluorobenzoyl chloride yielded the 1,4-addition product exclusively. The 13C chemical shifts for 2 are listed in Table 8.1. The key structural features in the FTIR spectrum of2 include the following absorptions aromatic C-H, 3074 cnr1, ketone C=0, 1658 cm-1, aromatic ether Ar—0—Ar, 1245 cm-1, and C—F, 1175 cm-1. 

Composite-pulse decoupling schemes like WALTZ [36, 37], DIPSI [38], or GARP [39], which are used in solution-state NMR, have failed to offer any significant improvements in the solid state compared to CW decoupling. The residual line width in CW-decoupled spectra is dominated by a cross term between the chemical-shielding tensor of the protons and the heteronuclear dipolar-coupling tensor [40, 41]. 

The normal Fourier transformed proton decoupled spectra of the solid elastomers were obtained on a Broker HX-90-E/SXP spectrometer with a 15-inch magnet. The solid samples were cut into small pieces and placed into the inner portion of a 7 mm ID Wilmad coaxial tube. The upper portion of the inner coaxial tube was 9 mm ID and fits precisely inside a standard 10 mm Wilmad tube which contained the high temperature lock compound. Depending on the desired temperature, either D2O, DMSO-de or 1,4-dibromotetra-deuterobenzene was used as the lock. Ninety degree pulse widths of less than 15 ps were used with a five second repetition time,... 

The isotope N, with a natural abundance of 99.9%, has nuclear spin 7 = 1 and gives broad signals which are of little use for structural determinations. The N nucleus, with I = 1/2, is therefore preferred. However, the low natural abundance of about 0.4% and the extremely low relative sensitivity (Table 1) make measurements so difficult that N NMR spectroscopy was slow to become an accepted analytical tool. A further peculiarity is the negative magnetogyric ratio since, in proton decoupled spectra, the nuclear Overhauser effect can strongly reduce the signal intensity. DEPT and INEPT pulse techniques are therefore particularly important for N NMR spectroscopy. 

In the case of isoorientin 6"-0-caffeate isolated from Gentiana arisanensis, the C NMR spectrum was assigned by H-decoupled spectra, DEPT pulse sequence, H- C COSY spectrum, long-range C- H COSY, and NOESY experiments the H NMR spectrum was analyzed with the aid of H- H COSY and H- C COSY. 

Although quaternary carbons do not appear on DEPT spectra, we can identify them by comparing DEPT and proton decoupled spectra. 

From the series of selectively decoupled spectra of glucose load the reference spectrum D NMRDATA GLUCOSE 1D H GHHD 001999.1R. From the Display pull-down menu choose the Multiple Display option. In the Select Multi Display Mode dialog box select all the seven spectra, starting with the reference spectrum. Click on the OK button to close the dialog box and initialize the multiple display. Click on the File Param. button and inspect the... 

D H/ H COSY Spectra OHHCO 001001-002001, OHHCODF 001001-002001 ID H H Homonuclear Decoupling Spectra OHHD 001001-006001... 

Figure 9.19—Proton decoupled 13C NMR spectrum of ethylbenzene. Each of the carbon atoms gives a signal consisting of a singlet. These large band decoupled spectra are simpler but contain less information.

Graphical analyses of series of single-frequency off-resonance decoupled spectra,... 

The signal assignments of the parent compounds 5 a- and 5 /i-androstane, 5 a- and 5 /i-pregnane and estrane [564] were performed by comparing the spectra with closely related derivatives, using substituent effects, off-resonance decoupled spectra and specifically deuterium-labeled analogues [564], The influence of different structural environments on the 13C chemical shift of the carbonyl carbon in keto steroids is illustrated by the values given in Table 5.10 [566]. The carbonyl carbon atom frequency in cyclopen-tanone moieties is shifted about 5 ppm downfield relative to that in cyclohexanone... 

Fig. 5.1 demonstrates for cholestane-3-one the utility of recording proton broadband-decoupled spectra, performing. /-modulated spin echo experiments, and generating subspectra from linear combinations of DEPT experiments for the unequivocal identification of primary, secondary, tertiary and quaternary carbon atoms. 

Comparison with the complete 13C NMR signal assignments of steroids enabled the interpretation of the 13C NMR spectra of structurally related cardenolides and sapogenins [596, 597]. Besides single-frequency off-resonance decoupling and low power noise decoupling, spectra of specifically deuterated compounds were used as additional aids for the signal identifications. The 13C chemical shifts are collected in Table 5.12 and the... 

C chemical shifts in aromatic compounds are dependent on the polarity of the substituent. Appendix 3, Table A3.14 shows the substituent effects for a range of substituted benzenes. The 13C spectra of substituted benzenes can often be interpreted on the basis of these substituent parameters in association with data from off-resonance decoupled spectra. 

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