F-Pentyl cation

The most stable of all alkyl cations is the t-butyl cation. Even the relatively stable f-pentyl and f-hexyl cations fragment at higher temperatures to produce the t-butyl cation, as do all other alkyl cations with four or more carbons so far studied.21 Methane,22 ethane, and propane, treated with super acid, also yield r-butyl cations as the main product (see 2-18). Even paraffin wax and polyethylene give f-butyl cation. Solid salts of t-butyl and f-pentyl cations, e.g., Me3C SbF4, have been prepared from super-acid solutions and are stable below -20°CP... 

Both computational and solvolysis studies have also been done to characterize the [ 5119] series of carbocations. The barrier to the hydride and methyl shifts that interconvert the methyl groups in the f-pentyl cation is 10-15 kcal/mol. This rearrangement must pass through a secondary ion or related bridged species. 

Figure 4. Degree of polymerization ( ) and polydispersity (O) resulting from cationic polymerizations of (a) 5-[(4 -(4"-cyanophenyl)phenoxy)pentyl]vinyl ether [125, 126] and (b) 8-((4 -(2/f,3S)-2-fluoro-3-methyl-pentyloxycarbonyl)-3 -fluorophenyl-4"-phenoxy)octyl] vinyl ether [ 139] initiated by triflic acid in CH2CI2 at 0 °C in the presence of dimethyl sulfide.

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