3- Methyl-3-pentyl cation

Cleavage to give a pentyl cation (m/z 71) and a methyl radical is weak because the methyl radical is less stable than a substituted radical. Cleavage to give a methyl cation (m/z 15) and a pentyl radical is not visible because the methyl cation is less stable than a substituted cation. The stability of the cation is apparently more important than the stability of the radical, since a weak peak appears corresponding to loss of a methyl radical, but we see no cleavage to give a methyl cation. 

A 1,3-hydride shift in a classical carbocation has been reported by Brouwer and van Doom (1969). The H-nmr spectrum of 2,4-dimethyl-2-pentyl cation [11] in FSOaH-SbFj-SOjClF at —117°C showed the a- and y-methyl groups at S 3.88 and 1.34 ppm respectively and the methylene resonance at 4.08 ppm. 

The NMR spectrum of 2,4-dimethyl-2-pentyl cation (42) in the temperature range from -110 to -70°C indicates rapid exchange of the nonequivalent methyl groups (Ea=8.5 kcal/mol)71. As the signal of the methylene protons remains unaffected, a direct 1,3 shift of hydrogen is the most plausible mechanism. Similar degenerate 1,4- and 1,5-hydrogen shifts have been shown to occur in (43) and (44), respectively. The relative rates decrease in the order 1,5>1,3>1,4—H shift. 

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. 

El elimination, 196-198, 201 Friedel-Crafts alkylation, 451 53, 479 SnI nucleophilic substitution, 143-146, 315-320,331 isopropyl cation, 141, 224 methyl cation, 141 iert-pentyl cation, 929 rearrangements, 187-189, 201, 219-220, 319-320,331,452,479 structure, bonding, and stability, 140-143, 162... 

The composition of a sample of commercial propene-oligomer gasoline (after hydrogenation) produced over solid phosphoric acid is illustrated in Fig. 4.16. The main products are liquid oligomers (di-, tri-, and tetramers) indicative of the high rate of the chain-transfer. The C9-carbons are predominandy doubly branched, consistent with cationic oligomerization. The structure of oligomers does not correspond exacdy to a simple reaction scheme due to skeletal isomerization. Thus, the dimers do not have exclusively the 2-methylpentyl skeleton, which is expected from the addition of the 2-propyl cation to propene. 3-Methylpentane and 2,3-dimethylbutane are also formed. The skeletons of these molecules may result from methyl shift in the 2-methyl — 3-pentyl cation. 

The cationic binuclear complex [(Mes3PAu)2Cl]BF4 has been found to catalyse the reaction of 2-methyl- or 2-pentyl-furan (78) with phenylacetylene, pent-l-yne, or hept-l-yne (79) to afford the products of a twofold hydroarylation of the alkyne (80).120... 

The same products were obtained in the solvolysis of 4-chlorospirohexane 1-methyl-bicyclo [2.1.0] pentyl p-nitrobenzoate, 1-cyclobutenylethyl tosylate and l-methyl-bicyclo[ 1.1.1] pentyl dinitrobenzoate, suggesting that the bicyclo [2.1.0]pentane-1-methyl cation is the common intermediate. 

---