DEPT 13C NMR

One-dimensional111 and 13C NMR experiments usually provide sufficient information for the assignment and identification of additives. Multidimensional NMR techniques and other multipulse techniques (e.g. distortionless enhancement of polarisation transfer, DEPT) can be used, mainly to analyse complicated structures [186]. 

In order to determine the structure and stereochemistry of compounds 36 and 37, standard H- HCOSY, H- C shift correlation (HETCOR), DEPT, and H NOE NMR experiments were performed. The 13C NMR spectrum of compound 36 is based on DEPT, HETCOR, and long-range H- C shift correlation experiments, which allowed the correct assignment of most of the carbon signals <1997MI328>. 

The carbon-13 NMR spectra of miconazole nitrate were obtained using a Bruker Instrument operating at 75, 100, or 125 MHz. The sample was dissolved in DMSO-d6 and tetramethylsilane (TMS) was added to function as the internal standard. The 13C NMR spectra are shown in Figs. 9 and 10 and the HSQC and HMBC NMR spectra are shown in Figs. 11 and 12, respectively. The DEPT 90 and DEPT 135 are shown in Figs. 13 and 14, respectively. The assignments for the observed resonance bands associated with the various carbons are listed in Table 4. 

The H NMR and the 13C NMR spectra of niclosamide were obtained using a Bruker Instruments system operating at 300, 400, or 500 MHz (proton NMR), or at 75, 100, or 125 MHz (carbon NMR). Standard Bruker software was used to obtain DEPT, COSY, and BETCOR spectra. All measurements were obtained with the compound being dissolved in deuterated dimethyl sulfoxide (DMSO-d6). 

Of the multitude of ID 13C NMR experiments that can be performed, the two most common experiments are a simple broadband proton-decoupled 13C reference spectrum, and a distortionless enhancement polarization transfer (DEPT) sequence of experiments [29]. The latter, through addition and subtraction of data subsets, allows the presentation of the data as a series of edited experiments containing only methine, methylene and methyl resonances as separate subspectra. Quaternary carbons are excluded in the DEPT experiment and can only be observed in the 13C reference spectrum or by using another editing sequence such as APT [30]. The individual DEPT subspectra for CH, CH2 and CH3 resonances of santonin (4) are presented in Fig. 10.9. 

The 13C NMR spectrum of 64, an amide of 63, showed sixty-two carbon signals of which partial assignments, shown in Table 16, were made based upon distortionless enhancement by polarization transfer(DEPT), H-13C correlation experiments and literature data describing 13C NMR analysis of polyene macrolides. 

The structure was determined by NMR spectral analysis including a variety of two-dimensional NMR techniques. The 500-MHz XH NMR spectrum of 77 taken in CDCI3 (Figure 26) revealed the presence of 5 aromatic protons, 15 olefinic protons, a methoxy (63.65), an allylic methyl (62.14) and a tertiary methyl group (61.33). The 13C NMR spectrum showed signals due to all 34 carbons, which were assigned to 7 quaternary carbons, 23 methines, 1 methylene and 3 methyls by DEPT experiments. The 13C and XH NMR spectral data are summarized in Table 27. 

IR spectra were taken on an Analect RFX-30 FTIR spectrophotometer neat between NaCI or KBr plates or as KBr disks. 1H NMR spectra were recorded on a Nicolet NT-360 (360 MHz) or on a Varian VXR-200 (200 MHz) spectrometer. All chemical shifts are reported in parts per million (8) downfield from internal tetramethylsilane. Fully decoupled 13C NMR spectra and DEPT experiments were recorded on a Varian VXR-200 (50 MHz) spectrometer. The center peak of CDCI3 (77.0 ppm) was used as the internal reference. 

The C NMR spectmm of 13 showed the resonances of all 35 carbon atoms. A combirration of broadband C-NMR and DEPT spectra indicated the presence of 7 methyl, 4 methylene, 16 methine and 8 quaterrrary carbon atoms in compound 13. Complete 13C-NMR chemical shift assignments of 13 are shown around structure 13. Based on these spectral data, structure 13 was established for this new compound. 

Assignment for C-6 changed due to recent results of 13C-NMR/DEPT experiments. 

The structure of the stable ozonide of a diterpene (300) was elucidated based on knowledge of the original structure assisted by H and 13C NMR spectroscopies. Thus, a 13C NMR DEPT experiment points to the presence of six quaternary C, six CH, three... 

FIGURE 13.26 13C NMR spectra of 1-phenyl-1-pentanone. (a) Normal spectrum, (b) DEPT spectrum recorded using a pulse sequence in which CH3 and CH carbons appear as positive peaks, CH2 carbons as negative peaks, and carbons without any attached hydrogens are nulled. 

WebSpectra includes 75 problems. All the problems display the 1H and 13C spectra, several with DEPT or COSY enhancements. A number include IR spectra. Organic Structure Elucidation contains 64 problems, all with 1H and 13C NMR, IR, and mass spectra. The exercises in both WebSpectra and Organic Structure Elucidation are graded according to difficulty. Give them a try. 

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