Carbenium cation

As for compounds 37, the rearrangements of 39 are considered to occur by a mechanism involving heterolytic N-C bond cleavage followed by in-termolecular recombination of the carbenium cation and benzotriazolyl anion so formed. 

Like the N-acetoxy arylamines, a reaction mechanism for N-sulfonyloxy esters would be expected to involve formation of a nitrenium/carbenium cation-sulfate anion pair which then reacts with... 

Scheme 7.19). Prototropic shift of the initial adduct to produce ROCHCl2 and, subsequently, the formate ester is a less favourable pathway. Alternatively, the carbon monoxide-separated ion-pair can lose a proton leading to an alkene, or cycloadducts derived from further reaction with the carbene. The formation of rearranged products from the reaction of 1 -hydroxymethyladamantane suggests that a relatively unencumbered carbenium cation can also be generated, which leads to a Nametkin rearrangement of the system [4]. 

A reaction in which atoms or molecules are taken up by a multiple bond is described as addition. The converse of addition—i.e., the removal of groups with the formation of a double bond, is termed elimination. When water is added to an alkene (la), a proton is first transferred to the alkene. The unstable carbenium cation that occurs as an intermediate initially takes up water (not shown), before the separation of a proton produces alco-... 

Clearly these examples also are in line with what is happening in hydrocracking. In acid-catalyzed hydrocracking cleavage of the larger saturated hydrocarbon chains can take place via p cleavage induced by carbenium cations formed via C—H protolysis, and also via direct C—C bond protolysis (Scheme 11.13). 

If, however, carbon anodes are used, the initial radicals RCHCH2N, are only weakly adsorbed and not stabilized in the adsorbed state. The adsorption of the intermediate radicals that are formed in consecutive steps is predominant and the adsorbed radicals are readily oxidized. The consecutive reactions of the carbenium cations then proceed according to heterogeneous kinetics at the surface of the carbon anode (218, 219). 

Thus contrary to the naive understanding, Pt does not catalyze but prohibits the thermodynamically favored oxidation, allowing for homogenous dimerization of the Kolbe radicals and similar radicals due to blocking the anode by a layer of adsorption-stabilized species, whereas C anodes allow for physisorption of radicals with subsequent immediate anodic formation of carbenium cations, which constitutes a completely different reaction path. 

The proportions of oxonium and carbenium ions in the chain growth, as well as their relative reactivities, may markedly depend on the polymerization coixlitions and vary with monomer structure. The high values of rate constants of the reaction between carbenium cations and ethers or acetals make questionable Okada s interpretation of the 1,3-dioxane-triethyloxonium salts system It is impossible to observe, at room temperature, the individual ROCHl species with excess of such nucleophiles as diethyl ether. We would rather suggest that the signal at 11—13 ppm 6 ( H-NMR) or 175—180 ppm 6( C-NMR) is due to some exchanging protonated species. 

If the cations are hydrogen ions (see Section 3.2.4.), guest molecules may add to them to give, for example, hydronium, ammonium, oxonium, or carbenium cations. The latter two may rearrange, and then decompose or dissociate to give product(s) which can leave the zeolite. Oxonium ions in particular are central to the most economically important processes of petrochemical industry. In simpler words, hydrogen zeolites are very important catalysts. 

Injection of ethene at 150°C or above produces a new infrared band at about 1500 cm (Figure 6), which is in the frequency range characteristic of partially unsaturated C-C bonds. Alkanes are detected in the gas phase above zeolites heated in the presence of ethene, and an intense absorption band appears in the ultraviolet-visible spectrum of ZSM-5 on heating in ethene to 100°C at 280 nm which has been attributed to an allyl carbenium cation (refs. 

Formation of such a species from alkenes requires hydride abstraction since ZSM-5 does not normally contain Lewis acid sites, this must involve alkyl carbenium cations ... 

P-09 - Activation of butanes with olefins carbenium cations over zeolite catalysts... 

A carbenium cation (R" ) formed as a result of the reaction can take... 

Mechanism of Alkane Reactions over Superacids.- Carbenium cations formed upon Brdnsted or Lewis superacid centre action can undergo isomerization. Two types of this reaction are possible. Firstly one in which the state of alkane branching is conserved and secondly one when it is changed. The example of the first... 

Such a transition state avoids involving the participation of the thermodynamically unfavoured primary carbenium cations as intermediates and explains the carbon atom exchange between certain... 

The carbenium cation formed as a result of olefin alkyl-... 

Salts with carbenium ions and SbFg as counteranion have already been described, such as magic methyl CHj SbFg. However, these super-electrophilic species can be involved in electrophilic additions to double bonds and carbenium cations, and are therefore not suitable for fluorination reactions. 

Lewis acids/co-catalyst combinations (TiCl4, AICI3, BF3/H2O) stable carbenium cations generated by the inifo- mediod Monomers 1,1 -substituted alkenes, styrenes, vinyl-ediers,... 

Nitrogen-containing compounds form an important class of N-bases due to their role in life processes. This is one of the reasons for our interest in reactions of free carbenium ions with amines [1-3]. In the course of these studies we found that, in contrast to the other N-bases, the interaction of carbocations with amines occurs via two competing channels, i.e. the formation of the condensation complex as a result of the overlap of the vacant p-orbital of the cation with the lone pair orbital of nitrogen and the proton transfer from the carbenium cation to the amine. The latter channel is very effective, due to the high proton affinities of amines. 

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