Cation reactivity

H-1 A ,3 -Thiazol-1 -ylideneacetic acid nomenclature, 1, 32 Thiazolylium cations reactivity, 6, 250... 

Carbocations as reactive intermediates play an essential role in organic reactions and have been thoroughly researched 102, l0J). The individual quality of the cationic polymerization results from the reproduction of the cationic reactive intermediate in every propagation step during the addition of monomers. 

Klingler and co workers—impact of metal coordination on the formate pathway. Klingler and coworkers114,125 carried out studies on the cation reactivity of formate in solution at 180 °C, 7.8 mol/L of H20 with the solvent triethylene glycol, and the formate concentration was varied. It was noted that formic acid produced from the carbonylation of water is catalyzed by hydroxide anion, and rapidly builds up to close to equilibrium concentration levels under these conditions, so that they had to use gold plated stainless steel autoclaves. They obtained a first order dependency of the water-gas shift reaction rate (i.e., H2 evolution rate) with formate concentration. As a control experiment, they added metal pentacarbonyl iron to the reactor, and observed no additional rate increase, indicating that the water-gas shift... 

The labels are based on organic and silicon-organic backbones. The simplest form of a label is nonreactive. Its only function is to enter and to hook to the channel. Nonreactive labels can be both neutral or cationic. Reactive labels enter the zeolite channels and then undergo a chemical reaction under the influence of irradiation, heat, or a sufficiently small reactant. In this way, they hook themselves inside the zeolite channels or, perhaps, bind to molecules already present. 

ELECTRON TRANSFER PHOTOCHEMISTRY OF CYCLOPROPANE SYSTEMS RADICAL CATION REACTIVITIES... 

VNP, and only homopolymer of polyl2-(cinnamoyloxy)ethyl vinyl ether] (PCEVE) was obtained. It seems that the cationic reactivity of the vinyl ether group in VNP was decreased because of the electron attracting nitro group attached at the 4-position on the phenoxide. 

Apart from some experiments with methyl and /i-chloroethyl vinyl ethers the initiator concentrations employed were such that the initiating cations, and presumably the propagating species, were essentially dissociated from the corresponding counterion. Once again therefore this data is a measure of the reactivity of the free polymeric cations derived from the various monomers. Isobutyl vinyl ether is the monomer most widely studied, and as would be anticipated for free cationic reactivities, the data varies little with the counterion employed (SbClg or BF4), or indeed with the carbocation used as initiator (C7H7 or Ph3C+) under similar experimental conditions. 

Photoproducts consistent with cationic reactive intermediates are also formed in the singlet excited state reaction of the allylic iodides geranyl and neryl iodide in n-hexane (equation 24)127. The favourable 2-Z geometry in neryl iodide leads to a larger proportion of the intramolecular alkylation product compared to the 1,4-HI elimination. Use of tetrahydrofuran instead of n-hexane promotes the formation of the cyclization products127, and so does the presence of Cu(I)57, which probably acts as a template. 

Treatment of a sulfoxide, particularly one with an anion-stabilizing substituent to help ylid formation, produces cations reactive enough to combine with nucleophiles of all sorts, even aromatic rings. The product is the result of electrophilic aromatic substitution (Chapter 22) and, after the sulfur has been removed with Raney nickel, is revealed as a ketone that could not be made without sul-... 

The chlorosulfonation of the CuPc system opens the door to the synthesis of reactive dyes, as shown in Fig. 13.137. In this case, aminochlorotriazine 56 reacts with a CuPc-S02Cl intermediate to give a mono-chlorotriazine reactive dye (57), which in turn can be used to make the cationic reactive dye 58. 

So far attempts to calculate exactly the cation-substrate energy state (cation reactivity) have been no more successful than in the case of radical reactivities, perhaps even less so. For some reactions, however, satisfactory agreement between theory and experiment has been obtained by semiempiri-cal methods [111]. The applied methods are not simple, and they have not been applied to polymerizations. 

Until recently, knowledge about absolute and relative rates of reaction of alkenes with carbocations was very limited and came almost exclusively from studies of carbocationic polymerizations [119-125]. The situation changed, when it became obvious that reactions of carbocations with alkenes do not necessarily yield polymers, but terminate at the 1 1 product stage under appropriately selected conditions (see Section III.A). Three main sources for kinetic data are now available Relative alkene and carbo-cation reactivities from competition experiments, absolute rates for reactions of stable carbocation salts with alkenes, and absolute rates for the reactions of Laser-photolytically generated carbocations with alkenes. All three sets of data are in perfect mutual agreement, i.e., each of these sets of data is supported by two independent data sets. 

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