Carbocations decomposition

When we turn to a secondary aliphatic diazonium ion, then loss of nitrogen to yield an unrearranged carbocation is an available pathway, so we get products of both diazonium ion decomposition and carbocation decomposition. We should thus expect to get less rearrangement from secondary than from primary aliphatic diazonium ions because this lower-energy pathway is available to the diazonium ion. 

Because a neutral molecule is eliminate4 rather than an anion, there is no electrostatic attraction (ion pairing) between the products of the dissociation step. As a result, the carbocations generated by diazonium-ion decomposition frequently exhibit somewhat different behavior from those generated from halides or sulfonates under solvolytic conditions. ... 

DFT molecular dynamics simulations were used to investigate the kinetics of the chemical reactions that occur during the induction phase of acid-catalyzed polymerization of 205 [97JA7218]. These calculations support the experimental finding that the induction phase is characterized by the protolysis of 205 followed by a rapid decomposition into two formaldehyde molecules plus a methylenic carbocation (Scheme 135). For the second phase of the polymerization process, a reaction of the protonated 1,3,5-trioxane 208 with formaldehyde yielding 1,3,5,7-tetroxane 209 is discussed (Scheme 136). 

The products obtained from DPM cracking in the present work agree with the results from the literature, mentioned in the Introduction, which indicate that the reaction proceeds via carbocation formation on acidic sites. This implies that the decomposition of DPM does not need the successive intervention of two catalytic sites, like in the "ideal hydrocracking" mechanism. Only acidic sites are sufficient to carry out the reaction. The improved activity of the mixtures when compared to the pure phases must therefore be explained differently. 

Carbenes from Sulfonylhydrazones. The second method listed in Scheme 10.8, thermal or photochemical decomposition of salts of arenesulfonylhy-drazones, is actually a variation of the diazoalkane method, since diazo compounds are intermediates. The conditions of the decomposition are usually such that the diazo compound reacts immediately on formation.147 The nature of the solvent plays an important role in the outcome of sulfonylhydrazone decompositions. In protic solvents, the diazoalkane can be diverted to a carbocation by protonation.148 Aprotic solvents favor decomposition via the carbene pathway. 

Alkanes are formed when the radical intermediate abstracts hydrogen from solvent faster than it is oxidized to the carbocation. This reductive step is promoted by good hydrogen donor solvents. It is also more prevalent for primary alkyl radicals because of the higher activation energy associated with formation of primary carbocations. The most favorable conditions for alkane formation involve photochemical decomposition of the carboxylic acid in chloroform, which is a relatively good hydrogen donor. 

Carbocations may be obtained from the decomposition of other cations, e.g. diazonium cations from the action of NaN02/HCl on RNH2 (cf. p. 119),... 

By protonation of alcohols The protonated alcohols give carbocations on decomposition. 

In addition to its interesting structure, the triethylsilylium-aromatic complex has proved useful in preparing other cations. Reaction with 1,1-diphenylethylene, for example, provided the cation 95, the first example of a persistent p-silyl substituted carbocation (i.e., where decomposition by loss of the silyl group did not occur). 

The decomposition of benzhydryltrimethylammonium hydroxide (Equation 4.5), on the other hand, according to Ingold, proceeds by initial slow formation of the relatively stable diphenylmethyl carbocation5 and subsequent fast attack on the carbocation by hydroxide. Because hydroxide, is not part of the activated complex of the slow step of this reaction, it does not enter into the rate equation. 

Activated alcohols are unstable, at least at high temperature, when the corresponding radicals are able to stabilize carbocations, for example in the case of allylic alcohols. The thermal decomposition of activated allylic alcohols leads to the formation of allylic chlorides. This decomposition can... 

The formation of ether has not been proved in this case, but the authors have proposed a decomposition mechanism including the heterolytic cleavage of an O-R bond and a subsequent attack of the carbocation formed on the oxygen atom of the neighboring OR-group [205]. 

Examples radioactive decay, unimolecular decomposition, SN1,E1 (carbocation), molecular rearrangement... 

The reactions of butane-2,3-diol by HCF in alkaline medium using Ru(III) and Ru(VI) compounds as catalysts leads to similar experimental rate equations for both the reactions. The mechanism involves the formation of a catalyst-substrate complex that yields a carbocation for Ru( VI) or a radical for Ru(III) oxidation. The role of HCF is in catalyst regeneration. The rate constants of complex decomposition and catalyst regeneration have been determined.89 A probable mechanism invoving formation of an intermediate complex has been proposed for the iridium(III)-catalysed oxidation of propane- 1,2-diol and of pentane-1,5-diol, butane-2,3-diol, and 2-methylpentane-2,4-diol with HCF.90-92 The Ru(VIII)-catalyzed oxidation some a-hydroxy acids with HCF proceeds with the formation of an intermediate complex between the hydroxy acid and Ru(VIII), which then decomposes in the rate-determining step. HCF regenerates the spent catalyst.93... 

The oxonium ion decomposes, generating a 3° carbocation and water. Because carbocations are planar, this decomposition destroys the steric hindrance effect that the t-butyl group created. 

The -deuterium KIE for the bromide and for the iodide ion reaction are significantly different and indicate that the nucleophiles are part of transition state of the rate-determining step of these reactions and the decomposition of the halides in chloroform occurs by way of an S 2 mechanism within a triple ion and not through carbocation formation. The kinetic study alone could not distinguish between the mechanistic alternatives, since the same kinetic expression would be obtained for all of the mechanisms. 

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