Interpretation of 13C NMR Spectra

The direct interpretation of 13C NMR spectra for complex hybrid structures may be very difficult. Sometimes, alkaline treatment may be helpful, as it eliminates the alkali-labile sulfate and increases the 3,6-anhydrogalactose content and, hence, the degree of polysaccharide regularity 424 If the sulfate groups are stable to alkali, it is necessary to... 

The assistance of Dr. K. W. Zilm in obtaining and assisting in interpretation of 13C NMR spectra is appreciated. The financial support of the State of Utah and U.S. Department of Energy is gratefully acknowledged. 

Interpretation of 13C-NMR spectra - the spectrum is that of all the carbon atoms in the molecule. It is easy to forget that the peaks for carbon atoms carrying no hydrogen atoms are present. 

Chen L, Robien W. Application of the maximal common substructure algorithm to automatic interpretation of 13C-NMR spectra. J Chem Inf Comput Sci 1994 34 934—941. 

General Analysis of trans fatty acids NMR spectra of lipids Guidelines for interpretation of 13C NMR spectra Applications of high-resolution methods to oils and fats Structure determination of polyunsaturated triacylglycerols 31P NMR for profiling of phospholipids 1998 (210) 1996(211) 1998(10, 18) 1999(212,213) 1999(213) 1998 (10) 1996(214) 1996(215)... 

Interpretation of H and 13C NMR spectra has been a part of almost all synthetic work on heteropyrans. Complete assignments using 2D NMR or other more advanced techniques still seem to be exceptional [92JCS(P2)1301]. Typical values of H and 13C NMR characteristics for some 2H- and 4//-heteropyrans are given in Tables V, VI, VII, and VIII. 

C 1-NMR spectroscopy is the method of choice for determining the molecular structure of polymers in solution [230]. Polyolefin 13C NMR is mainly quantitative ID 1-NMR multiple pulse techniques are used for spectral interpretation. The resolution obtained in 13C NMR spectra of LDPE is an order of magnitude larger than in the corresponding 1H-NMR spectra... 

Lounasmaa et al. (152) have analyzed the 13C-NMR spectra of several 4-benzyltropane alkaloids. The analyses and the stereochemical conclusions were based on the preliminary correct interpretation of the 13C-NMR spectra of 3a-benzoyloxytropane (14) and 3/f-benzoyloxytropane (43), and of their hydrolyzed counterparts 3a-hydroxytropane (1) and 3/ -hydroxytropane (40), respectively. The chemical shifts of 4-benzyltropanes and 4-hydroxybenzyl-tropanes (100-103,105-107,109,110,220-223) (Fig. 7) are listed in Table X. 

The 13C NMR spectra of the three isomeric difluorobenzenes are distinctive and interpretable upon inspection, with the 1,2-isomer exhibiting three signals, the 1,3-isomer four, and the 1,4-isomer two. (Figs. 3.23-3.25). The signal observed in each of these 13C spectra at -128.3 ppm derives from the solvent, benzene-d6. 

In contrast, 13C nmr spectra of ring-substituted /J-bromocumyl cations [2] can be unambiguously interpreted in terms of open /1-bromocarbocations, since the ring substituent effects on the chemical shifts are similar to those on the corresponding non-brominated cations [1], even for the electron-attracting p-trifluoromethyl group (Olah et al, 1972). 

In the 13C-NMR spectra of the 2-alkyl-1,3,5,5-tetramethylhexahydropy-rimidines (328), the lower field absorption of the axial 5-methyl carbon in the 2-isopropyl and 2-tert-butyl derivatives than in 328 (R = Me or R = Et) has been interpreted in terms of flexible nonchair conformations for 328 (R = iPr and t-Bu).92... 

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... 

From the data given in Table 5.38 b the following guidelines can be set up, which are helpful for the interpretation of the 13C NMR spectra of new flavonoids ... 

Exercise 9-43 Figure 9-50 shows the 1H and 13C nmr spectra of a compound C6H10O. With the aid of these spectra, deduce the structure of C6H10O. It will be seen that the 13C spectrum is quite simple, even though the proton spectrum is complex and difficult to interpret. 

At first glance, some of the above summary would seem to discourage the use of 13C spectra. However, the ingenious remedies for these difficulties have made l3C NMR spectrometry a powerful tool, as this chapter will confirm. In fact, side-by-side interpretation of 13C and H spectra provide complementary information. 

The spectral analysis is carried out manually because automatic interpretation and library programs are normally not available. Difficulties in NMR and automatic interpretation are (a) high spectral background in spectra recorded from environmental samples, often leading to resonance overlap, (b) solvent dependence of chemical shifts (8), which with couplings affects the appearance of the spectrum, and (c) in the case of H NMR spectra, the complexity. The other spectra, particularly 13C H, are simple, but low sensitivity is then a problem. 

NMR spectra have been used frequently to elucidate and/or confirm the structures of these heterocycles, but little or no systematic study had been done. A detailed study of l3C NMR spectra by distortionless enhancement by polarization transfer (DEPT), inverse H-I3C coherence transfer experiments (HMQC and HMBC) and by INADEQUATE of factor F0 has been reported <91JBC9622>. The 13C NMR spectra of a series of pyrido[4,3-J]pyrimidines were interpreted on the basis of a detailed study of other analogues <91JCS(P2)1559>. Carbon-13 NMR spectroscopy has been used to indicate the site of alkylation of pyrido[2,3-c]pyridazin-4-ones <90CPB3359>. 

The ultimate value of any type of spectroscopy depends on our ability to interpret accurately the spectroscopic data we acquire. These data are usually plotted as a spectrum, which is nothing more than a graph of intensity versus frequency (also called position) for each signal. In this chapter we will examine and interpret the actual H and 13C NMR spectra of toluene. 

Interpretation of Spectra. Spectra of the peracetate derivatives in deutero-chloroform were recorded at 80 MHz for protons and 20 MHz for carbons using a Varian FT80A spectrometer. Assignments for the H- and 13C-NMR spectra of the resorcinol, phloroglucinol, and catechin reaction products, summarized in Tables I and II, respectively, are largely drawn from previously reported results (5,[Pg.187]

---