Subject carbon capture

The thermal neutrons are also subject to capture by the slowing material. While carbon and beryllium have very small capture cross sections for thermal neutrons, 70 and deuterium still smaller, an appreciable fraction of thermal neutrons (about 10 percent of the neutrons present in the system under best conditions with graphite) is lost by capture in the slowing material during diffusion therethrough. It is therefore desirable to have the neu-73 irons reaching thermal energy promptly enter uranium. 

Many groundwaters are contaminated with the cleaning solvents trichloroethylene (TCE) and perchloroethylene (PCE). They are two of the most common organochlorine compounds found in Superfund sites. Radiation-induced decomposition of TCE in aqueous solutions has been the subject of several recent studies [15-20]. In most of the referenced studies, the complete destruction of TCE was observed. Dechlorination by a combination of oxidative and reductive radiolysis was stoichiometric. Gehringer et al. [15] and Proksch et al. [18] have characterized the kinetics and mechanism of OH radical attack on TCE and PCE in y-ray-irradiated aqueous solution. Trichloroethylene was readily decomposed in exponential fashion, with a reported G value of 0.54 pmol J-1. A 10 ppm (76 pM) solution was decontaminated with an absorbed dose of less than 600 Gy. For each OH captured, one C02 molecule, one formic acid molecule and three Cl- ions were generated. These products were created by a series of reactions initiated by OH addition to the unsaturated TCE carbon, which is shown in Eq. (45) ... 

Steric factors have been mentioned they are not expected to play a major role. In fact, several radical cations have been captured by attack on highly congested centers [154, 156]. The ring-opening substitution of tricyclane radical cation, 81 +, occurred exclusively at the tertiary carbon [215] whereas that of 82 occurred at the tertiary carbon further removed from the dimethyl-substituted bridge, i.e., at the less hindered of two tertiary carbons, not at the quaternary carbon [216]. These results clearly show that the nucleophilic substitution at the cyclopropane one-electron bond is subject to conventional steric hindrance and is not subject to inverse steric effects [154]. 

The precise role of base additives in promoting C-H activation has been the subject of several computational studies. Clot and Baudoin used B3PW91(DMF) calculations to study the reactions of 2-halo-ferf-butylbenzene (8) at PdfPRg) species to form cyclobutarenes (9) (Figure 1.4a). These studies compared a model system (with R = Me) to those with the bulky phosphines used experimentally (R = Bu [14, 15] or Cyp [16]). With R = Me and Bu, the initial Ar-Br oxidative addition and subsequent C-H activation and C-C reductive elimination steps were all compared in the presence of three different bases (OAc, HCOg", and C03 ). Experimentally, use of C03 " proved most efficient. Calculations on the PMe3 model failed to capture this preference for carbonate and, moreover,... 

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