Ad E mechanism

The Ad -E mechanism proposed to account for the kinetics of substitution of 9-(a-bromo-a -arylmethylene)fluorenes by thiolate ions in aqueous acetonitrile also features elimination of the leaving group in a fast step following rate-determining carbanion formation (by nucleophilic addition). ... 

The reactions of / -ketoethynyl- and ) -amidoethynyl(phenyl)iodonium triflates, 17 and 18, with sodium / -toluenesulfinate illustrate the synthetic potential of alkynyliodonium salts33. Although the direct attachment of a carbonyl group to the / -carbon atom of the triple bond in alkynyliodonium ions might be expected to facilitate alkynyl sulfone formation via the Ad-E mechanism, this mode of reactivity has not been observed. Instead, the MC pathway with carbenic insertion dominates and affords sulfones containing the... 

The production of the (Z)-haloalkenes is thought to proceed via initial exchange of the tetrafluoroborate and halide ions and collapse of the resulting vinyliodonium halides by the addition-elimination (Ad-E) mechanism (equations 203 and 204)84. As with Ad-E reactions of moderately activated vinyl halides (X = Cl, Br), which typically occur with configurational retention (> 95%)143 145, the intermediate carbanions apparently prefer a least motion rotation of 60° prior to the expulsion of iodobenzene. It has been demonstrated by an NMR study that anion exchange between (Z)-(2)-phenylsulfonyl-l-decenyl)-phenyliodonium tetrafluoroborate and tetrabutylammonium chloride occurs instantaneously in deuteriochloroform84. Furthermore, when authentic halide salts of the... 

The production of CLS by the melt dispersion technique is based on the melting of the lipid core material together with the lipophilic agent (i.e., phospholipids). Afterward, a warm aqueous solution is added to the molten material and is mixed by various methods (i.e., mechanical stirring, shaking, sonication, homogenization). Then the preparation is rapidly cooled until lipid solidification and the formation of particle dispersion. This method was used by Olbrich et al. [19] to produce the cationic solid lipid nanoparticles to use as novel transfection agent. 

An attempt to study resolved ((/i)-18) as a probe for the detailed mechanism of the Ad -E vinylic substitution reaction has been complicated by intervention of a competing reaction route this is believed to involve a competing (E cB elimination-addition, for which antiperiplanar orientation of H and Cl is not a requirement.7 a-Deuterated (ca 50%) E- and Z-substitution products (which do not themselves exchange deuterium) are obtained on reaction with MeS in 9 1 CD3CN-D2O but no incorporation of deuterium in unreacted ((E)-18) occurs and neither does isomerism to ((Z)-18) precede elimination. 

A ceramic matrix composite or CMC is composed of two or more solids, the matrix of which consists of a ceramic material or carbon. The crystalline, ceramic matrix is moulded and/or densified at a temperature of at least 1000 K. To the matrix one ormore solid inorganic substances are added, e.g. in the form of particles or fibres in order to alter the (thermo) mechanical properties of the pure matrix. In the composite s microstructure these additives can still be distinguished by their chemicalcomposition or geometry even after they have undergone a temperature treatment of at least 1000 K. 

Schulte-Frohlinde D (1986) Comparison of mechanisms for DNA strand break formation by the direct and indirect effect of radiation. In Simic MG, Grossman L, Upton AD (eds) Mechanisms of DNA damage and repair basic life science Vol 38. Plenum Press, New York, pp 19-27 Schulte-Frohlinde D, Bothe E (1990) Determination of the constants of the Alper formula for singlestrand breaks from kinetic measurements on DNA in aqueous solution and comparison with data from cells. Int J Radiat Biol 58 603-611... 

The usual description of these different polymerization processes suggests that all produce stable latexes and various hypotheses have been advanced to explain the stability of these latexes to such factors as added electrolyte, mechanical shear and freezing and thawing. In the literature, there is little mention of the fact that many of these polymerizations produce varying amounts of coagulum, i.e., polymer recovered in a form other than that of a stable latex. This coagulum is produced in all sizes of polymerization reactors, ranging from the smallest laboratory... 

In order to explain the results, the term adduct-mediated electron transfer (AMET) was introduced. This term implies that it is the adduct which mediates electron transfer. However, the adduct does not mediate ET but its heterolysis constitutes the ET. Furthermore, the allegation of a distinction between ET and AMET creates a mechanistic dichotomy which is unnecessary. It is possible to explain all the results on the basis of a single (unified), i.e., the ad-el mechanism. 

In 1 reactions the solvent usually operates as the attacking base. If a base is added, the mechanism can be pushed into the E2 region. Preparatively useful examples use OH", OR" or NH2", with their conjugate acids as solvents. A highly concentrated strong base moves the mechanism towards E cB and a weak base in a polar aprotic solvent promotes an E2 mechanism. 

When the p-carbon of the vinyl group bears two substituents, retention of configuration is now observed as a result of a ligand coupling mechanism. However, an alternative mechanism involving addition-elimination (Ad-E) cannot be formally excluded. 

Another class of aluminium compounds used in e-caprolactone polymerization are aluminium porphyrins. In two studies the use of (5,10,15,20-tetraphenylporphinato)-aluminium alkoxides (TPPAIOR) was evaluated Living polymerization of e-caprolactone and 5-valerolactone could be achieved. It was established that a major improvement in polymerization rate was obtained if an inert Lewis acid was added, e.g. TPPAICP . The polymerization proceeds then by the mechanism shown in Eq. 9-10. 

---