Benzyl cations 1 -phenyl-2- ethyl

Due to the benzylic p-Tc resonance stabilization the C+-C,pso bond has partial double bond character and the ortho, ortho and meta, meta methine groups syn and anti to the silyl group are non-equivalent. The effect pf the a-silyl group on the positive charge in benzyl cations can be estimated by comparison of the NMR spectroscopic data of the 1 -phenyl-1 -(trimethylsilyl)ethyl cation 1 with those for the 1-phenylethy 1 cation 5 (P) and the cumyl pation 3 (15, 16, 17) (Table 1). 

The effect of an w-silyl group on the positive charge in benzyl cations can be estimated by comparing the NMR spectroscopic data for the 1 -phenyl- 1-trunethylsilylethyl cation 290 with those for the phenyl ethyl cation 78 and the cumyl cation 292 prepared under identical conditions from the corresponding chlorides with Sbl 5. The 1II and 13C NMR data for 78, 290 and 292114 measured under comparable conditions are given in Tables 10 and 11. 

It is known that for SnI ewaction (substitution-nucleophilic-unimolecular) [140-141] a key intermediate is a carbocation, therefore the more reactive substrate will be the one that can produce the most stable carbocation. The reactivity of methyl, ethyl, 2-propyl, and 2-methyl-2-propyl tosylates under SnI reaction conditions is inversely proportional to the calculated hydride affinity of the corresponding carbocations. The calculated values were in agreement with the experimental findings which were obtained through solvolysis rate measurement of these tosylates under SnI conditions [142, 143]. Correlation of the cation stability-hydride and affinity-solvolytic rate of the reaction under Sn 1 reaction conditions was observed for the allyl cation (allyl, 3-penten-2-yl, and 2-methyl-3-butene-2-yl cations)[144] and the benzyl cation (benzyl, 1-phenylethyl, and 2-phenyl-2-propyl cations) [145] series. The most reactive substrates were the ones that formed the carbocations with the lowest hydride affinity. 

Hyperbranched polymers were prepared from 3-(l-chloroethyl)-ethyl benzene by cationic pol)mierization [77], and from 4-[2-(phenyl)-2-(l-2,2,6,6-tetramethylpiperidinyloxy)ethyloxy]methyl styrene [78] or / -(chloromethyl)-styrene [79] by free radical polymerization. In the cationic living polymerization, the benzylic chloride of 3-(l-chloroethyl)-ethyl benzene is activated with SnCl4 in the presence of Bu4NBr [80,81], followed by low-temperature living... 

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