Carbon isotopes spectroscopy

Not long ago this could have been determined only by extremely laborious, and often equivocal, selective degradation experiments but the coming of carbon n.m.r. spectroscopy has now made all the difference. Neither the 12C nor the 14C carbon isotopes produce an n.m.r. signal but the 13C isotope, which occurs in ordinary carbon to... 

William Schopf studied supercrustal rock samples from Akilia Raman and ion microscopic photographs showed the presence of carbon-containing inclusions in grains of apatite. The carbon isotope ratio was determined by secondary ion mass spectroscopy (SIMS) the 813C value was -29% 4%, in agreement with earlier analyses. This in turn confirmed the values obtained by Mojzsis (1996), which had been questioned by Lepland et al. three years later. The final verdict on the oldest fossils in western Greenland may not be reached for several years yet (McKeegan et al., 2007 Eiler, 2007). 

Giraudon, S., Danzart, M., and Merle, M. H. (2000). Deuterium nuclear magnetic resonance spectroscopy and stable carbon isotope ratio analysis/mass spectrometry of certain monofloral honeys.. AOAC Int. 83,1401-1409. 

Recently, it was shown that ss-NMR spectroscopy can be used to determine the conformation of EpoB in the solid state [116]. The method relies on the measurement of intramolecular short H-H distances (in the range 1.8-3.0 A) from 2D CHHC correlations under MAS [117]. Regarding the sample preparation, a small amount of 13C labeled compound was diluted with EpoB with natural abundance of carbon isotopes. This reduces the signal to noise but, on the other hand, it excludes contributions from intermolecular H-H polarization transfer. Under these conditions, all CHHC cross-peaks result from intramolecular polarization transfer and reflect intramolecular interproton distances. 

Carbon and nitrogen are detectable by NMR as the isotopes 13C and 15N. These have a low natural abundance (1.1% and 0.37%, respectively) and thus are suitable for labeling studies. The naturally abundant carbon isotope, 12C, is not detectable as it has zero spin. The naturally abundant nitrogen isotope, 14N, has spin but is not detectable in a 15N experiment as it has a different gyromagnetic ratio. Furthermore, 14N is not as useful as 15N for NMR spectroscopy since, with a few exceptions, it gives much broader resonances. Both 13C and 15N show abroad chemical shift range which aids signal resolution and identification. 

Isotopes in stars Relative numbers of the two isotopes of carbon have been measured in a large number of stars by the spectroscopy of the 5-micrometer vibration-rotation band of the CO molecule, which differs for each carbon isotope owing to the different mass on one end of the CO dumbbell. These show that in red-giant stars the isotope 13C often varies with respect to the abundance of 12C. These variations are... 

V. Caer, M. Trierweiler, G.J. Martin, M.L. Martin (1991) Determination of site-specific carbon isotope ratios at natural abundance by carbon-13 nuclear magnetic resonance spectroscopy. Anal. Chem. 21, 2306-2313... 

Crown ethers, of caUxarenes 1396-1399—see also Cahx[4]crowns Cryptands—see Calixcryptands Crystal effects, on LD IR spectroscopy 368 Crystal stmcture determination, computer-based 549 C—S bond fission, homolytic 1079 Cumene, as substrate for antioxidants 859 4-Cumyl-l-naphthol, formation of 607 Cumyloxyl radical 877 Cumylphenols, formation of 607 4-Cumylresorcinol, formation of 607 Curcumin 867, 868, 870 Curie-point carbon-isotope-ratio mass spectrometry 303 Curie-point Py/GC/MS 303 Curie-point pyroUzer 938 p-Cyanophenol,... 

Based on comparison of data from UV, fluorescence, and NMR spectroscopy, and from carbon isotope determination for humic substances isolated from coastal and open ocean environments, the authors have concluded the following (1) other than its metal complexation and redox functions, the only resemblance between humic substances from open ocean (marine) and terrestrial environments is that they are both colored organic acids soluble in water, and (2) marine humic substances are formed in situ and only in the coastal zone is there an admixture of terrestrially derived humic substances from rivers. However, this second conclusion has not yet been reconciled with the observations discussed by Mayer in Chapter 8 that riverine humic... 

In view of this universal knowledge about proton and carbon NMR spectroscopy within the chemical community, it is remarkable that heteronuclear NMR is still looked npon as something of a curiosity. Admittedly, most organic compounds contain only nitrogen, oxygen, and sulfur atoms, as well as the obligatory hydrogen and carbon atoms, elements that have an unfavourable isotope distribution when it comes to NMR spectroscopy. Each of these three elements has a dominant isotope i N (99.63% natural abundance), 0 (99.76%), and (95.02%), with O, S, and... 

Most of the development work on molecular markers (MMs) has resulted from the use of GC-MS, but with advances in other techniques it is clear that this field will benefit from making greater use of alternative identification methods, such as Fourier transform infrared spectroscopy and nuclear magnetic resonance techniques. Isotopic measurements can now be used to obtain complimentary information on the history and origin of a sample. It is now possible to perform a forensic investigation using stable carbon isotopic analyses on individual MMs by GC-Isotope Ratio MS without prior isolation of com-... 

NMR spectroscopy has developed to such an extent that it has become the most useful method for the elucidation of the conformation of peptides in solution. It can also identify the amino acid sequence in medium size peptides. The method is based on the magnetic properties of the nuclei of isotopes with spin numbers I = 1/2. Of these the proton ( H), the carbon isotop C, and to a lesser extent are of practical importance. 

New possibilities for such purity examinations have opened up with the development of C-resonance spectroscopy. By means of this method it is now possible to distinguish between carbon atoms in different chemical environments. In accordance with the above considerations, this may be utilized for qualitative investigations. It should be noted, however, that the sensitivity of the carbon-resonance method is lower than that of proton-resonance spectroscopy. Owing to the low abundance of the isotope, the measurements must be carried out in more concentrated solutions. At the same time, the resolution of carbon-resonance spectroscopy is higher than that of proton-resonance spectroscopy, hence the former can be used for the detection of impurities (when present in sufficiently high... 

Sturchio, N.C. (2004) Use of table chlorine and carbon isotope analysis in environmental forensic investigations of groundwater contamination. Abstracts from PIIT CON— Analytical Chemistry and. Applied Spectroscopy Conference Chicago, USA (March 7-12, 2004). 

Whitesell, J.K. (James K.) Stereochemical analysis of alicyclic compounds by C-13 NMR spectroscopy. Bibliography p. 1. Nuclear magnetic resonance spectroscopy. 2. Carbon—Isotopes—Analysis. 3. Stereochemistry. 

The way the spins of the protons and neutrons in the nucleus combine can lead to nuclei with spin quantum numbers (/), varying from 0 to 6, and isotopes of the same element can have, and usually do have, different spin quantum numbers. Isotopic nuclear spin is important in NMR. For example, has I — 0 and has I = A, so that NMR spectroscopy is not possible with nuclei but is possible with Fortunately for chemists the natural carbon isotopes include 1 % and NMR is a very important tool in chemical structure elucidation [14]. Nuclear spin can also have subtle effects in other spectroscopies [15], and nuclear mass is important in molecular vibrational and rotational spectroscopies. 

Amines - Spectra. 2. Alkaloids — Spectra. 3. Carbon - Isotopes — Spectra. 4. Nuclear magnetic resonance spectroscopy. I. Hindenlang, David M., joint author, n. Title. 

C NMR (Section 13.14) Nuclear magnetic resonance spectroscopy in which the environments of individual carbon atoms are examined via their mass 13 isotope. 

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