Carbocations, continued stabilized

Tripheny(methyl cation (10 ) is effectively stabilized by electron donating substituents. B. W. Laursen et al. reported the highly stable carbocation 11+ with a pKr+ value of 19.7 (10). Recently, they reported a similar carbocation with a much higher p R+ value (23.7) (11). In our continuing efforts to prepare extremely stable carbocations, we have investigated the effect of introduction of electron donating substituents into each azulenyl group. 

The tertiary carbocation can now act as an electrophile and attack the alkene to form another tertiary carbocation of similar stability and reactivity to the first. So the polymerization continues. 

The difficulties encountered in using the analysis of substituent effects in solvolyses as a mechanistic probe mostly arise from the mechanistic involvement of the solvent (Shorter, 1978, 1982 Tsuno and Fujio, 1996). Consequently, the behaviour of benzylic carbocations in the gas phase should be the best model for the behaviour of the solvolysis intermediate in solution (Tsuno and Fujio, 1996). The intrinsic substituent effects on the benzylic cation stabilities in the gas phase have also been analysed by equation (2), and they will be compared here with the substituent effects on the benzylic solvolysis reaction. In our opinion, this provides convincing evidence for the concept of varying resonance demand in solvolysis. Finally, we shall analyse the mechanisms of a series of benzylic solvolysis reactions by using the concept of a continuous spectrum of varying resonance demand. 

Iated with each other, we will continue to talk about carbocation stabilities in a qualitative sense. 

For obtaining a cationic polymerization, the new carbocation generated between R and the monomer should have enough stability to be relatively easily formed and to continue the polymerization (for example, CH2=CH2 is not polymerized using a cationic initiator, while (CH3)2C=CH2 can be polymerized because the species RCH2-C(CH3)2 is stable enough to be formed). The stability of the carbocation increases as the chain length increases. Chain transfer reactions are common in carbocation polymerization. The termination reactions typically occur because of the combination of the cationic component with a counterion. 

Whatever the explanation of the stabilization of carbanions by CN may be, new manifestations of this continue to be found, e.g. the behaviour of C(CN and C(CN)2N02 as the leaving groups in the generation of the -cumyl and -butyl carbocations, respectively, by C—C bond fission . ... 

Protolytic ionization of methylcyclopentane gives an equilibrium mixture of the tertiary 1-methyl-1-cyclopentyl cation (29) (more stable by about 40 kJ/mol) and the secondary cyclohe l cation (32) (Scheme 5). At low temperature, irreversible reaction of 29 with CO leads to ion 30, which, after reaction writh ethanol, gives the 31 ester. Product composition, in this case, reflects the difference in stability of the intermediate carbocations. Since the carbonylation step is reversible at higher temperature, and carbocation 32 has a much higher affinity for CO, the concentration of 33 in solution continuously increases to yield, after quenching with ethanol, the 34 ester. This is an example of a kinetically controlled product formation through a thermodynamically unfavorable intermediate. 

The bromine radical then adds to the double bond to give the more stable radical. Radical stability broadly follows carbocation stability, so the stable species is the tertiary rather than the secondary radical (Figure 11.41). This tertiary radical then abstracts a hydrogen from HBr to regenerate the bromine radical. We describe this as a radical chain reaction—once started, the reaction should continue without further initiator. The steps of Figure 11.40 are described... 

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