Carbon-13 NMR spectrum

For complex molecules that give unresolved H spectra, cross-sections of COSY spectra may be taken, giving a set of one-dimensional spectra. In these, signals that overlap in the conventional H spectrum are often separated in different cross-sections where they can be seen clearly for their multiplet structure. An example is given in the work of Portlock et al. [26] 

The abundant C isotope has no nuclear magnetic moment, but the C isotope, with 1.1% natural abundance, does [6,27]. The signal from these carbons, however, is only th the intensity from the same number of hydrogens. These two factors cause a carbon spectrum to be about th the intensity of a hydrogen spectrum of the same sample. This necessitates the use of pulsed irradiation and Fourier transform methods and summation of many repeated spectra (Section 10.5.1). Typically the spectra are obtained at 2-10 s intervals and, for a routine 5-20-mg sample, less than 15 min is required to accumulate a good summation. 

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Bouquet, M. and A. Bailleul (1986), Routine method for quantitative carbon 13 NMR spectra editing and providing structural patterns. Application to every kind of petroleum fraction including residues and asphaltenes . Fuel, Vol. 65, p. 1240. 

Tetramethylsilane (TIMS) (Section 13 4) The molecule (CH3)4Si used as a standard to calibrate proton and carbon 13 NMR spectra... 

Proton and carbon-13 nmr spectroscopy provides detailed information on all types of hydrogen and carbon atoms, thus enabling identification of functional groups and types of linkages ia the lignin stmcture. Detailed a ssignments of signals ia proton and carbon-13 nmr spectra have been pubHshed... 

The spin-lattice relaxation time, T/, is the time constant for spin-lattice relaxation which is specific for every nuclear spin. In FT NMR spectroscopy the spin-lattice relaxation must keep pace with the exciting pulses. If the sequence of pulses is too rapid, e.g. faster than BT/max of the slowest C atom of a moleeule in carbon-13 resonance, a decrease in signal intensity is observed for the slow C atom due to the spin-lattice relaxation getting out of step. For this reason, quaternary C atoms can be recognised in carbon-13 NMR spectra by their weak signals. 

Figure 13.6 Carbon-13 NMR spectra of 1-pentanol, CH3CH2CH2CH2CH2OH. Spectrum (a) i a single run, showing the large amount of background noise. Spectrum lb) is an average of 200 runs.

Figure 13.8 Carbon-13 NMR spectra of (a) 2-butanone and (b) para-bromoacetophenone.

W. Wehrli and T. Wirthlin, Interpretation of Carbon-13 NMR Spectra, Heyden and Son, London, 1978. 

A collection of 500 C NMR spectra is found in Johnson and Jankowski, Carbon-13 NMR Spectra , Wiley, New York, 1972. 

The proton decoupled carbon 13 NMR spectra for three poly( cyclohexylmethyl-co-isopropylmethyl) copolymers are shown in Figure 4. The backbone methyl group is observed as occurring between -4 and -1 ppm and consists of multiple resonances which are due to polymer microstructure. Multiple resonances are also observed for the methyl and tertiary carbon of the isopropyl group and for the methine carbon of the cyclohexyl group. Microstruc-tural assignments for these resonances remain to be made. It has also been found that increasing the bulky character of the substituent yielded broader resonance peaks in the carbon-13 NMR spectra. 

Figure 4. 67 MHz Carbon-13 NMR Spectra for PolyCcyclohexyl-methyl-co-n-propy1-methylsilane) Copolymers.

Fig. 36. Proton-decoupled natural-abundance carbon-13 NMR spectra of some corrinoids at 15.08 MHz, obtained by the Fourier transform method, (a) 0.67 M aqueous dicyano-cobinamide. (b) 0.024 M aqueous cyanocobalamin. (c) 0.038 M 5 -deoxyadenosylcobalamin (compliments of A. Allerhand)...

Previous authors have taught the principles of solving organic structures from spectra by using a combination of methods NMR, infrared spectroscopy (IR), ultraviolet spectroscopy (UV) and mass spectrometry (MS). However, the information available from UV and MS is limited in its predictive capability, and IR is useful mainly for determining the presence of functional groups, many of which are also visible in carbon-13 NMR spectra. Additional information such as elemental analysis values or molecular weights is also often presented. 

Polymer Characterization. Proton NMR spectra at 300 MHz were obtained from a Varian HR-300 NMR spectrometer. Deutero-benzene and spectrograde carbon tetrachloride were used as solvents. The concentration of the polymer solutions was about 1-5%, Carbon-13 NMR spectra were obtained from a Varian CFT-20 NMR spectrometer, using deuterochloroform as the solvent for the polymers. The concentration of the solutions was about 5%. Chemical shifts in both proton and carbon-13 spectra were measured in ppm with respect to reference tetramethylsilane (TMS). All spectra were recorded at ambient temperature. 

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. 

Quin, L.D. and Littlefield, L.B., Importance of the structure of the phosphorus functionality in allowing dihedral angle control of vicinal 13C-31P coupling. Carbon-13 NMR spectra of 7-substituted bicyclo[2,2,l]heptane derivatives,. Org. Chem., 43, 3508, 1978. 

Proton-noise decoupled and single-frequency off-resonance decoupled carbon-13 NMR spectra were determined for the CTC Working Standard (Figure 13). 

The spectrum is in substantial agreement with the data reported by Wenkert et. al, (6). However, on the basis the proton coupled carbon 13 NMR spectra, the assignments for 6 and 7ot are reversed [Brambilla (16)] from those previously reported. The new assignments are based on long range H-C-O-C couplings. 

Wehrli, FW, and T. Wirthin., Interpretation of Carbon-13 NMR spectra , London, Heyden, 1976 Abraham, RJ, and P. Loftus., Proton and Carbon-13 NMR spectroscopy , London, Heyden, 1978 Levy, GC, RL Lichter, and GL Nelson, Carbon-13 Nuclear Magnetic Resonance, 2nd, ed., New York, Wiley-Interscience, 1980. 

Sadder Standard Carbon-13 NMR Spectra Sadder Research Laboratories Philadelphia,... 

Further confirmation of the structure of the AHLs often follows from the determination of their proton and carbon-13 NMR spectra. A large number of AT-acyl, AT-(3-oxoacyl) and AT-(3-hydroxyacyl)-L-HSL derivatives have been prepared and their NMR data reported [14-16]. Also a detailed study by Lao et al. [49] on the complete assignments of the 13C NMR resonances of AT-acyl and N-(3-oxoacyl)-L-HSL derivatives has been published. These assignments were made by comparison with values for AT-butanoyl-L-HSL (C4-HSL), whose structure was comprehensively established by a combination of 1-D and 13C spectra and 2-D COSY,NOESY, HSQC and HMBC experiments. The assignments... 

Carbon-13 NMR spectra. A carbon-13 NMR spectrum of HTE polymer (Rn S 500) is shown in Figure 3. The carbon-13 NMR spectra of HTE polymers show the carbon chemical shifts at 79.3 and 72.7 ppm for the backbone and the terminal methine carbons respectively, at 43.9 and 46.2 ppm for the backbone and the terminal chloromethyl carbons, respectively, and in the range of 69.7-72.0 ppm as a multiplet for the methylene carbon. It is a characteristic feature of hydroxyl-terminated polyethers that the terminal carbon exhibits a up-field shift due to the substituent effect of the hydroxyl group, whereas the (0 carbon(s) to the terminal hydroxyl group exhibits a down-field shift (Table III). The terminal methine carbon also suggests that the hydroxyl groups are predominantly secondary. 

Vanderlei MF, Silva MS, Gottlieb HF, Braz-Filho R. Iridoids and Triterpenes from Hi-matanthus phagedaenica the Complete Assignment of the Proton and Carbon-13 NMR Spectra of Two Iridoid Glycosides. Journal of the Brazilian Chemical Society 1991 2(2) 51-55. 

Figure 1. Carbon-13 NMR spectra (in DMSO-ds) of steam-exploded aspen lignins (a) EXWL (b) EXBWL and (c) TomL.

Carbon-13 NMR spectra were obtained using a JEOL FX90Q operating at 22.5 MHz for carbon. Spectra were obtained using 75° pulses and a 4 sec. delay between pulses with complete proton decoupling. The samples were analyzed in 10 mm tubes. 

J-resolved two-dimensional carbon-13 NMR spectra [60, 61] separate chemical shifts and coupling constants in the two-dimensional JCH, <5C plane. Their practical value can be estimated on looking at Fig. 2.52. In the one-dimensional 13C NMR spectrum of... 

Carbon-13 NMR spectra of the H2C On series, such as deltic, squaric, croconic and rhodizonic acids, obtained in anhydrous solvents [304] display carbonyl shifts similar to those reported for quinones (Table 4.33). Considerable shielding of the carbonyl carbon of deltic acid diethyl ester is not only attributed to the three-membered ring but also to an electron releasing effect of the ethoxy groups. 

Carbon-13 NMR spectra of all nitro compounds are characterized by quadrupolar broadening of the a carbon signal. 

Detailed reviews [470-475] have dealt with numerous investigations of organometallic compounds and transition metal complexes using carbon-13 as NMR probe. Looking at the data selected in Tables 4.71 and 4.72, it is seen that some important features must be considered when recording and evaluating carbon-13 NMR spectra of organometallic compounds. 

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