Isotope carbon

Carbon 12, the most abundant naturally occurring isotope, has zero spin and thus cannot be studied by NMR. On the other hand, its isotope carbon 13 has an extra neutron and can be its low natural occurrence (1.1%) nevertheless makes the task somewhat difficult. Only pulsed NMR can be utilized. 

Carbon has seven isotopes. In 1961 the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis for atomic weights. Carbon-14, an isotope with a half-life of 5715 years, has been widely used to date such materials as wood, archaeological specimens, etc. 

One mole is the number of atoms in exactly 12 g of the pure isotope carbon-12. 

This new and novel method to study the photochemical degradation of Kevlar-29 fabric in air divides into four steps (1) fabric cleaning, (2) photolysis at specified temperature and time in 0.2 atm - 02, (3) preparation of the degraded (DMAc-soluble) sample surface for decarboxylation at 25° and 196°C in the concentrated sulfuric acid, and (4) the total carbon dioxide analyses by gas chromatography and the isotopic carbon dioxide ( °C02 and 48co2) ratios by GC-mass spectrometer. 

Two of these isotopes, carbon-12, the most abundant, and carbon-13 are stable. Carbon-14, on the other hand, is an unstable radioactive isotope, also known as radiocarbon, which decays by the beta decay process a beta particle is emitted from the decaying atomic nucleus and the carbon-14 atom is transformed into an isotope of another element, nitrogen-14, N-14 for short (chemical symbol 14N), the most common isotope of nitrogen ... 

An extensive general account of conventional techniques with isotopic carbon has been given by Murray and Williams (104). 

Radiocarbon years are calibrated from determinations of the 14C activity and stable isotopic carbon ratios of dendrochrono-logically dated tree rings [4]. The stable isotope data are required to normalize the dates to average wood with 613C value of -25 per mil (13C/12C fractionation relative to PDB reference standard). Photosynthetic and other plant physiological processes may produce differential isotopic fractionation between species, within the same species in different localities and even within the same tree under changing environmental conditions. 

The average atomic weight for carbon is 12.011 because about 1 % of carbon found in nature is the isotope, carbon 13, having an extra neutron in the nucleus. 

An important benefit of the isotopic approach is that below-ground biomass values are not required. The 13C natural abundance isotopic carbon budget approach is based on C3 plants having lower 13C value than C4 plants (Ehleringer 1991 Clay et al. 2006) and that the signatures can be tracked by placing C3 plant residue into a soil derived from C4 plants or vice versa. In these calculations, several definitions are needed. These definitions include... 

It will readily be seen in our series of w-fluorocarboxylic acids, that when n is odd, / -oxidation would yield the toxic fluoro-acetic acid, whereas when n is even, the compound would presumably be oxidized only as far as the non-toxic yff-fluoro-propionic acid.1 The pharmacological results obtained are in complete accord with this hypothesis, and provide verification, of a kind not hitherto achieved, of the process of / -oxidation in the living animal body. However, Weinhouse, Medes and Floyd2 have inoculated rat-liver slices with one or two fatty acids containing isotopic carbon, and have obtained some evidence for a process of /7-oxidation. 

And so it happened that the detection of isotopic carbon from UC02 in the [i carboxyl group of a-ketoglutarate was celebrated as a discovery of CO 2 fixation in animal tissues, and was taken as evidence that there wasn t any citric acid in the citric acid cycle. A citric acid precursor of a-ketoglutarate would have to be labelled as in compound 1... 

Higmhi, T. Studies of Lignin using Isotopic Carbon X [cf. (2.5)]. Formation of Lignin from Phenylpropanoids in Tissue Culture of White Pine. Canad. J. Biochem. Physiol. 40, 31—34 (1962). 

Elements are defined by the number of protons in the nucleus of each atom. The number of nuclear protons is equal to the number of electrons orbiting the nucleus. The nucleus of carbon contains six protons. This value is known as the atomic number for carbon. In nature, carbon occurs largely in a form in which the nucleus also contains six neutrons. The atomic mass of carbon is defined as the sum of the number of protons pins neutrons. Consequently, this form of carbon is called carbon-12, or About 98.9% of carbon in nature is Most of the rest is carbon-13, and contains seven neutrons in the nncleus. Smaller amounts of carbon occur that contain five or eight neutrons. These are known, respectively, as carbon-11, and carbon-14, These variations on the theme of carbon are called isotopes. Carbon-11 and carbon-14 are radioactive and decay spontaneously carbon-12 and carbon-13 are stable. 

The Lawrence Berkeley Laboratory and other groups were unable to confirm the spontaneous-fission reaction of Ku-260, so the Dubna groups discovery was disputed. The Berkeley equipment was unable to accelerate neon ions to the speeds required to produce Ku-260, and thus they tried a different reaction in a new automated rapid chemistry apparatus that identified and confirmed new isotopes of heavy metals. The procedure involved bombarding the element californium-239 with a mixture of the isotopes carbon-12 and carbon-13 ions, as follows ... 

Elemental carbon has many important applications. The diamond is a precious gem, known to mankind for ages graphite is used as an electrode and has numerous other applications carbon-14 isotope is used in carbon dating and the isotope carbon-13 in tracer studies and NMR. Carbon black is used in paints, pigments and inks. Activated carbon is used as an adsorbent for purification of water and separation of gases. Coke is used for electrothermal reduction of metal oxides to their metals. These applications are discussed below in more detail. 

Radiocarbon dating relies on the fact that carbon exists naturally in several isotopic forms. All of them are virtually identical chemically, but they can be distinguished with special methods of analysis. One isotope, carbon-14, provides a kind of elemental clock that reveals the age of carbon-rich materials from living organisms. This technique is one of the most valuable of the many uses that chemists, geologists, medical biologists, and other scientists have found for isotopes the sibling forms that every element displays. 

Scientists commoniy use the isotope carbon-14 as a tooi to determine the age of objects composed of materiai that was once aiive. Determining the age of something using carbon isotopes is caiied carbon dating, or radiocarbon dating. 

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