Cleavage 656 REACTION INDEX

Eisch et al. (24) performed a mechanistic study of the desulfurization of dibenzothiophene by a nickel(0)-bipyridyl complex and reported that a radical anion of the thiophene nucleus was formed and underwent C-S bond cleavage into S and an aromatic radical. In addition, they suggested that the oxidative reaction of the nickel(0)-bipyridyl complex toward dibenzothiophene had the characteristics of stepwise electron transfer rather than nucleophilic attack. However, no correlations occurred between the desulfurization rate and the reaction indexes of Fr(E), Fr(N), and Fr(R), as shown in Table II. The results suggested no evidence for either electron transfer or nucleophilic attack in this study. Moreover, the radical reaction was not... 

CONTENTS Preface. Patrick S. Mariano. Intramolecular Photochemical Electron Transfer (PET) Induced Bond Cleavage Reactions in Some Sulfonium Sal Derivatives. Frar kiin D. Saeva. Aspects of Electron Transfer Promoted Stil-bene Photocycloaddition Reactions. Kevin Peters. Mechanistic and Synthetic Aspects of Amine-Eone SET Photochemistry, Ung Chan Yoon and Richard S. Givens. Index. 

The low reactivity of aliphatic ethers renders the problem of the preparation of suitable crystalline derivatives a somewhat difficult one. Increased importance is therefore attached to the physical properties (boding point, density and refractive index) as a means for providing preliminary information. There are, however, two reactions based upon the cleavage of the ethers which are useful for characterisation. 

The catalytic efficiency of an enzyme is indicated by its kcatIKM value, the value combining the effectiveness of both the productive substrate binding and the subsequent conversion of substrate molecules into product (Copeland, 2000). This value is the apparent second-order rate constant for enzyme action under conditions in which the binding site of the enzyme is largely unoccupied by substrate. The kcatIKM value is the index for comparing the relative rates of cleavage of alternative, competing substrates. The KM is the Michaelis constant, an apparent dissociation constant and hence a measure of substrate affinity. This value equals the concentration of substrate needed to reach half maximum velocity of the enzyme reaction. 

---