Spin-accelerated reactions

Rate acceleration is the most fimdamental aspect of catalysis. To elucidate the electronic mechanisms of spin-acceleration phenomena therefore represents an important topic in both bioinorganic and biomimetic dioxygen activation 5,122). Many other t5rpes of substrate transformations catalyzed by metal complexes or redox enzymes also involve key steps with a change in spin along their reaction coordinates. The abimdance of such phenomena seems to be much wider than initially thought. This... 

Generally, the rate of heat transfer is low near the burner wall because the temperature differences are very small. (Load movement is counterflow to flame movement thus, the flame reactants are coolest as they leave any one zone whereas the load pieces are hottest as they leave any one zone.) As the distance from the burner wall increases, the load surface is colder and the flame temperature is hotter because the combustion reaction rate accelerates. However, a control T-sensor 15 ft (4.6 m) from the burner wall limits the furnace temperature at that point. (This temperature is held to a setpoint determined by the operator or by a model.) With high-spin burners, as one follows the temperature profile away from its maximum and in the direction of flame reactant flow, the furnace temperature declines quickly to the setpoint, and thereafter drops rapidly to the exit. 

Fig. 3.6 (a) Decay scheme of and (b) ideal emission spectrum of Co diffused into rhodium metal. The nuclear levels in (a) are labeled with spin quantum numbers and lifetime. The dashed arrow up indicates the generation of Co by the reaction of Mn with accelerated deuterons (d in Y out). Line widths in (b) are arbitrarily set to be equal. The relative line intensities in (%) are given with respect to the 122-keV y-line. The weak line at 22 keV, marked with ( ), is an X-ray fluorescence line from rhodium and is specific for the actual source matrix... 

Spectroscopic developments have accelerated advances in the field of catalysis. This volume analyzes the impact on catalyst structure and reactivity of EXAFS, SIMS, MSssbauer, magic-angle spinning NMR (MASNMR), and electron-energy-loss vibrational spectroscopy. Many of these techniques are combined with other analytical tools such as thermal decomposition and temperature-programmed reactions. 

The photochemical acceleration of a variety of other reactions involving Al(Por)R is observed, and as a result, the mechanism of this photochemical activation is important and was the subject of two studies. In the first, a spin trap (tributylnitrosobenzene) was added to Al(TPP)Et in the dark, and slow production of Et (trapped as ArN(Et)0 ) was observed by EPR spectroscopy. Upon irradiation the amount of this product increased and a signal corresponding to the Al—O... 

Tripathi GNR (1998) Electron-transfer component in hydroxyl radical reactions observed by time resolved resonance Raman spectroscopy. J Am Chem Soc 120 4161-4166 TsaiT, Strauss R, Rosen GM (1999) Evaluation of various spin traps for the in vivo in situ detection of hydroxyl radical. J Chem Soc Perkin Trans 2 1759-1763 Tsay L-Y, Lee K-T, Liu T-Z (1998) Evidence for accelerated generation of OH radicals in experimental obstructive jaundice of rats. Free Rad Biol Med 24 732-737 Ulanski P, von Sonntag C (2000) Stability constants and decay of aqua-copper(lll) - a study by pulse radiolysis with conductometric detection. Eur J Inorg Chem 1211-1217 Veltwisch D, Janata E, Asmus K-D (1980) Primary processes in the reactions of OH radicals with sul-phoxides. J Chem Soc Perkin Trans 2 146-153... 

The -CN radicals appear to dimerize rapidly to produce dicyanogen, NCCN. ) The reduction rate of [TPPFe (CN)2] depends on a variety of factors. Light and increased cyanide concentrations accelerate the reduction, while small amounts of water inhibit the reaction. Reoxidation of the dicyano Fe complex by molecular oxygen leads directly to the formation of the low-spin complex, as opposed to IJ.-OXO dimer formation, because of the presence of excess strong-held ligand (i.e. the reaction with O2 is probably outer-sphere). Autoreduction of a series of dicyanoiron(III) porphyrins studied by White-Dixon showed that... 

Fig. 13. Energy curves along the reaction coordinate of a spin-forbidden two-state process (a). In such a situation, spin crossover can accelerate product formation by opening up a novel low-energy reaction pathway (b). Adapted from Ref 121).

Spin system, 157, 159 Splitting, Zeeman, 154 Stability study, accelerated, 260 Standard potential, 254, 359 Standard reaction, 315 Standard state, 253 selection of, 208 Stationary-state hypothesis, 101 Statistical analysis, 40 Statistical analysis of solvent effects,... 

Photolysis of ketones in micelles with simultaneous application of an external magnetic field permits a C isotope enrichment. (Cf. Section 6.1.5.5.) This is the case because C nuclei have a magnetic moment and thus accelerate the spin inversion by the hyperfine interaction mechanism. (Cf. Example 4.9.) Due to the more efficient recombination of radicals containing C, the initial product formed after photolysis in a back reaction is C enriched (TUrro et al., 1980b). 

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