Carbon natural isotopes

The two most common isotopes of oxygen are and 0, and the two natural isotopes of hydrogen are and or D (deuterium). If a sample of carbonate contains Cis moles of and Ci6 moles of then define the heavy light ratio as Ris = Cia/Cie- Similarly, natural water molecules are mostly of three types H O, H] 0, and HD O. For a given sample of water, call the number of moles of each W, W g, and Wq, respectively. Then define the heavyriight ratios as ki8 = Wig/VV and Rp = WqIW. For either water or carbonate, the 5 are defined as deviations of these ratios from standard values for these ratios (call the ratios of the standards Sig and Sq) ... 

Carbon-13 spectra are inherently less complex than proton spectra for two reasons, viz. (a) chemical shifts between 13C nuclei in different chemical environments can differ by as much as 200 ppm whereas proton shift differences are seldom more than 10 ppm (b) as the natural isotopic abundance of 13C is only 1.1%, coupling between 13C nuclei themselves is not observed (but see 2-D INADEQUATE spectrum, p. 420). 

Example Isotopic enrichment is a standard means to enhance the response of an analyte in nuclear magnetic resonance (NMR). Such measures gain importance if extremely low solubility is combined with a large number of carbons, as is often the case with [60]fullerene compounds. [19] The molecular ion signals, IVT, of Qo with natural isotopic abundance and of C-enriched Cgo are shown below (Fig. 3.11 for EI-MS of [60]fullerenes cf. Refs. [20-22]). From these mass spectra, the enrichment can be determined by use of Eq. 3.1. For Qo of natural isotopic abundance we obtain Mrceo = 60 x 12.0108 u = 720.65 u. Applying Eq. 

Applications to Biological Samples. - Methods of distance measurements were compared for four doubly spin-labelled derivatives of human carbonic anhydrase.53 The distances between the spin labels were obtained from continuous wave spectra by analysis of the relative intensity of the half-field transition, Fourier deconvolution of the line-shape broadening, and computer simulation of line-shape changes. For variants with interspin distances greater than 18 A, the DEER method also was used. For each variant, at least two methods were applicable and reasonable agreement between distances obtained by different methods was obtained. The useful distance ranges for the techniques employed at X-band with natural isotope abundance spin labels were estimated to be half-field transition (5-10 A), line-shape simulation (up to 15 A), Fourier deconvolution (8 - 20 A), and four-pulse DEER (> 18 A).53... 

Thus, the mass observed for the molecular ion of CO, for example, is the sum of the exact formula masses of the most abundant isotope of carbon and of oxygen. This differs from a molecular weight of CO based on atomic weights that are the average of weights of all natural isotopes of an element (e.g., C = 12.01, O = 15.999). 

Another combination of magnetic and electric sector fields, together with a tandem accelerator, is realized in different types of accelerator mass spectrometers (AMS)17 applied for carbon-14 dating and extreme ultratrace analysis of long-lived radionuclides at natural isotope abundances (see Chapter 5). 

The atomic mass unit (amu) is defined as 1/12 the mass of a carbon-12 isotope. The relative atomic mass of an element is the weighted average of the isotopes relative to I/12(of jhe carbon-12 isotope. For example, the atomic mass of neon is 20.17 amu and is calculated from the following data neon-19 (amu of 19.99245, natural abundance of 90.92%), neon-20 (amu of 20.99396, natural abu dan c of 0,260%) and ncon-21 (amu of 21.99139, natural abundance ofc 82%) ... 

Carbon-14 is a natural isotope of carbon. It is also a radioisotope, which means that it is radioactive. Radioisotopes break down, or decay, in a specific amount of time. The amount of time it takes for half of the atoms of a radioisotope to decay is called its half-life The half-life of carbon-14 is about 5,700 years. 

Cotte, J. F., Casabianca, H., Lheritier,J., Perrucchietti, C., Sanglar, C., Waton, FI., and Grenier-Laustalot, M. F. (2007). Study and validity of 13C stable carbon isotope ratio analysis by mass spectrometry and 2H site-specific natural isotopic fractionation by nuclear magnetic resonance isotopic measurements to characterize and control the authenticity of honey. Anal. Chim. Acta 582,125-136. 

Figure 11. Data documenting the calibration of the carbonate clumped-isotope thermometer for inorganic calcite grown in the laboratory (filled circles) and aragonitic corals grown in nature at known temperatures (an example of one of several biogenic materials we have also calibrated unfilled symbols). The large, gray circle shows the result of analyses of a modern soil carbonate collected from the Bolivian Altiplano plateau. The horizontal position of this data point is based on the mean annual surface temperature near the site of collection between 2004 and the present.

Jiang G, Kennedy MJ, Christie-Blick N (2003) Stable isotopic evidence for methane seeps in Neoproterozoic postglacial cap carbonates. Nature 426 822-826... 

Natural isotopes of carbon and their solar abundances... 

The study of the fiillerenes by C NMR spectroscopy is not straightforward. C has a low natural isotopic abundance (1.11%) and a low relative receptivity. In addition, the carbon atoms in fiillerenes have relatively long relaxation times and spectra for the higher, less symmetric fiillerenes can only be obtained within a reasonable time by using paramagnetic relaxation reagents, typically Cr(acac)3. 

The carbonyl-carbon kinetic isotope effect (KIE) and the substituent effects for the reaction of lithium pinacolone enolate (112) with benzaldehyde (equation 31) were analyzed by Yamataka, Mishima and coworkers ° and the results were compared with those for other lithium reagents such as MeLi, PhLi and AllLi. Ab initio (HF/6-31-I-G ) calculations were carried out to estimate the equilibrium isotope effect (EIE) on the addition to benzaldehyde. In general, a carbonyl addition reaction (equation 32) proceeds by way of either a direct one-step polar nucleophilic attack (PL) or a two-step process involving electron transfer (ET) and a radical ion intermediate. The carbonyl-carbon KIE was of primary nature for the PL or the radical coupling (RC) rate-determining ET mechanism, while it was considered to be less important for the ET rate-determining mechanism. The reaction of 112 with benzaldehyde gave a small positive KIE = 1.019),... 

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