Primary tritium

The primary tritium KIE (k /l ) and the secondary tritium KIE ( h/ h) were determined in two different experiments carried out in the following way. If Ra is the radioactivity of the original reactant and / ROh is the radioactivity of ROH (ROT) determined at low (<5%) extents of reaction, the primary tritium KIE is given by equation (52). If the radioactivity of the styrene isolated at low extents of reaction, Rs, is also measured, the secondary tritium isotope effect can be calculated from (53). 

The observation of a primary tritium isotope effect (H/T) that is substantially larger than the value predicted on the basis of the semiclassical Swain-Schaad relation (Chart 3) from a heavy-hydrogen (DAT) isotope effect. The same information can be expressed in terms of a Swain-Schaad exponent required to relate the two isotope effects that is substantially larger than the semiclassical value of 3.26. 

Isotope effects have also been applied extensively to studies of NAD+/NADP+-linked dehydrogenases. We typically treat these enzymes as systems whose catalytic rates are limited by product release. Nonetheless, Palm clearly demonstrated a primary tritium kinetic isotope effect on lactate dehydrogenase catalysis, a finding that indicated that the hydride transfer step is rate-contributing. Plapp s laboratory later demonstrated that liver alcohol dehydrogenase has an intrinsic /ch//cd isotope effect of 5.2 with ethanol and an intrinsic /ch//cd isotope effect of 3-6-4.3 with benzyl alcohol. Moreover, Klin-man reported the following intrinsic isotope effects in the reduction of p-substituted benzaldehydes by yeast alcohol dehydrogenase kn/ko for p-Br-benzaldehyde = 3.5 kulki) for p-Cl-benzaldehyde = 3.3 kulk for p-H-benzaldehyde = 3.0 kulk for p-CHs-benzaldehyde = 5.4 and kn/ko for p-CHsO-benzaldehyde = 3.4. 

If a much larger area heat exchanger is used, considerable improvement is possible. For example, if the 25,600 m heat exchanger has its tubes reduced in radius and coiled, perhaps 100 times more area could result. Using the 0.65 ran thick TH Cr-1 Mo, and cold trapped NaK on the secondary side results in a primary tritium pressure of 0.12 mPa or 8.7 x 10 Torr (29 wppm or 23 kg in a 1630 m liquid lithium blanket). 

Primary tritium isotope effects have been determined by Schilf et alP at various temperatures for proton-nitrogen couplings in two Schifif bases obtained by the condensation of 4-methoxy- and 4,6-dimethoxysalicylaldehyde with methylamine. However, the results are not conclusive and it is not clear if they can be used as an additional probe of the hydrogen bond character. 

Primary tritium isotope effect 849 Propellanes, synthesis of 569, 570 Protecting groups for thiols 432 acetamidomethyl 675, 676 acetyl and benzoyl 677, 678 benzyl 671, 672 benzyloxycarbonyl 678 benzylthiomethyl and phenylthio-methyl 681... 

Primary tritium isotope effects can also be measured. As tritium is radioactive, this requires that the NMR tube is protected from breaking in the NMR instrument Referencing in this case can be either ghost referencing [15] or the use of CgHgT versus C5Hg [16]. 

The primary tritium and deuterium isotope effects were found to be 0.91 and 0.62 ppm, respectively, again suggesting either a very strong hydrogen bond or a tautomeric equihbrium. 

Primary isotope effects, AT, can of course be also measured for tritium although it is experimentally more difficult to produce tritiated compounds because of the health hazards involved. However, a large survey has shown that primary tritium isotope effects are proportional to AD [31]. Primary isotope effects were early on pointed out as a means of distinguishing between double... 

AH operating facilities shear the spent fuel elements into segments several centimeters long to expose the oxide pellets to nitric acid for dissolution. This operation is often referred to as chop-leach. The design and operation of the shear is of primary importance because (/) the shear can be the production botdeneck, and (2) the shear is the point at which tritium and fission gases are released. 

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

Nuclear Reactions. The primary reaction for the production of tritium is... 

Production in Target Elements. Tritium is produced on a large scale by neutron irradiation of Li. The principal U.S. site of production is the Savaimah River plant near Aiken, South Carolina where tritium is produced in large heavy-water moderated, uranium-fueled reactors. The tritium may be produced either as a primary product by placing target elements of Li—A1 alloy in the reactor, or as a secondary product by using Li—A1 elements as an absorber for control of the neutron flux. 

A special type of substituent effect which has proved veiy valuable in the study of reaction mechanisms is the replacement of an atom by one of its isotopes. Isotopic substitution most often involves replacing protium by deuterium (or tritium) but is applicable to nuclei other than hydrogen. The quantitative differences are largest, however, for hydrogen, because its isotopes have the largest relative mass differences. Isotopic substitution usually has no effect on the qualitative chemical reactivity of the substrate, but often has an easily measured effect on the rate at which reaction occurs. Let us consider how this modification of the rate arises. Initially, the discussion will concern primary kinetic isotope effects, those in which a bond to the isotopically substituted atom is broken in the rate-determining step. We will use C—H bonds as the specific topic of discussion, but the same concepts apply for other elements. 

TABLE 11. The primary hydrogen-tritium kinetic isotope effects found in the reactions between various alkyl radicals and tributyltin hydride and tributyltin hydride-t... 

More experimental data where the secondary KIE was larger than the EIE were subsequently published by Subramanian and Saunders (1984). The 2-arylethyl system was employed in these studies because other relevant data, such as the primary deuterium KIE, were available for this reaction. Special techniques were developed to determine the primary and the secondary tritium KIEs for this system. Three isotopically distinct elimination reactions (49-51) are possible for a 2-arylethyl derivative tracer labelled with tritium at the 2-position. 

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