Butyl cations carbon scrambling

Sometimes intermediates like [6] undergo hydride shift to another comer protonated cyclopropane (7). This is another mechanism by which carbon scrambling can be achieved, i.e. through a combination of methide- and hydride shifts. Together with 1,2-hydride shifts, such a mechanism accounts for the complete degeneracy of the 2-butyl cation [7]. Vinyl cations substituted... 

Such an intermediate explains the - C scrambling in the butane carbon chain without the formation of isobutane ring opening at the C3 — C2 carbon bond results in the formation of x-butyl cation, whereby the labeled C is no longer a terminal carbon ... 

Protonated methylcyclopropanes are considered to be involved in the carbon scrambling of the 2-butyl cation which occurs (Scheme 18) with a measured activation energy of 7.5 kcalmol" a value in good agreement with the calculated energy difference... 

When the isopropyl cation 2 was generated from 2-chloropropane with 50 percent 13C enrichment of C—2 in S02C1F—SbFs at 60 °C, equilibration of the 13C lable occurred with a half-life of 1 hour. After several hours, the 13C was distributed equally among the three carbons. This observation suggests involvement of proton-ated cyclopropanes in the carbon scrambling process (see subsequent discussion). Similar scrambling was observed in the secondary butyl 14 (sec-butyl) and r-amyl cations 4 (Saunders)33. ... 

It was shown that the t-butyl cation undergoes degenerate carbon scrambling at... 

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