Benzyl cation substituted

The Yukawa-Tsuno r values have been measured for the solvolysis reactions fonning benzyl cations and several a-substituted derivatives, 6-3IG charges and bond orders have been calculated for the presumed cationic intermediates. Analyze the data for relationships between r and the structural parameters. (Hint. Plot r versus the bond orders and the charges at C-1, C-2, C-3, and C-4.)... 

Indeed, cumyl carbocations are known to be effective initiators of IB polymerization, while the p-substituted benzyl cation is expected to react effectively with IB (p-methylstyrene and IB form a nearly ideal copolymerization system ). Severe disparity between the reactivities of the vinyl and cumyl ether groups of the inimer would result in either linear polymers or branched polymers with much lower MW than predicted for an in/mcr-mediated living polymerization. Styrene was subsequently blocked from the tert-chloride chain ends of high-MW DIB, activated by excess TiCU (Scheme 7.2). 

Furfuryl alcohol in an acid medium gives rise to reactions of polycondensation reactions of successive electrophilic substitutions involving furan molecules. This reaction is identical to the reaction described for benzyl alcohol on p.256 and represents the same dangers. It is carried out under the same conditions, ie in a sulphuric medium. The electrophilic species that comes into play is very similar to the benzyl cation. 

Benzyl Alcohols. Benzyl alcohols of nearly all kinds undergo reduction when treated with acid in the presence of organosilicon hydrides. The most obvious exception to this is the behavior of benzyl alcohol itself. It resists reduction by the action of trifluoroacetic acid and triethylsilane, even after extended reaction times.26 Reducing systems consisting of triethylsilane and sulfuric acid/acetic acid or p-toluenesullonic acid/acetic acid mixtures also fail to reduce benzyl alcohol to toluene.134 As previously mentioned, substitution of boron trifluoride for trifluoroacetic acid results in the formation of modest yields of toluene, but only when a very large excess of the silane is used in order to capture the benzyl cation intermediate and suppress Friedel-Crafts oligomerization processes.129,143... 

P-silyl substituted benzyl cations, 151-152 cyclobutadienyl dication, 150... 

The xylenes are produced in an equilibrium mixture containing 24% p-, 54% m-, and 22% o-xylene (11) This is readily understandable. The transalkylation occurs via an electrophilic substitution of toluene by a benzyl cation. In the absence of steric constraints, p- and o-xylene are expected as predominant... 

In this connection the case of cyclopropylalkyl cation and substituted cyclopropyl cations is interesting. Cyclopropylmethyl cation has been found to be more stable than benzyl cation and the stability increases with each addition of cyclopropyl groups. Thus... 

Scheme 2 Regiospecific formation of /3-silyl substituted benzyl cations...

Anodic side chain substitution is a competing reaction to nuclear substitution of aromatic compounds. In side chain substitution, the first formed acidic radical cation is deprotonated at the a-carbon atom of an alkyl group to form a radical. This is further oxidized to a benzyl cation, which reacts with a nucleophile (Scheme 9, path d). The factors that influence the ratio of nuclear to side chain substitution have been described in 5.4.1. 

The semiempirical AMI MO method has been used to calculate heats of formation of a series of m- and p-substituted benzene and toluene derivatives ArY and ArCHaY, and their phenyl or benzyl cations, anions, and radicals heterolytic and homolytic bond dissociation energies (BDEs) and electron transfer energies for the ions have also been calculated and the relationship A//het = A//et-I-AWhomo has been confirmed (it being noted that A//homo is insensitive to ring substituents). The linear relationship found between and the appropriate HOMO or LUMO... 

Energies for various possible arenium ions and regioisomeric benzylic cations were computed at the DFT B3LYP/6-31G(d) level or by AMI for comparison with the experimental results. These findings provided further evidence in support of the stability sequence 1-pyrenyl > 4-pyrenyl > 2-pyrenyl in a-pyrene-substituted carbocations as models for the intermediates arising from BaP-epoxide ring opening (Fig. 10). 

Acidolysis of benzylic C-O bonds becomes easier with increasing stability of the corresponding benzylic cation. The sensitivity of benzylic linkers towards acids can therefore be fine-tuned by varying the substitution pattern on the arene. Electron-donating substituents will increase the sensitivity towards acids, whereas electron-acceptors will diminish acid-sensitivity. This order of reactivity towards electrophiles... 

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