Isopropyl cation geometries

Isopropyl alcohol, photoxidation, 41 238-239 Isopropyl cation, 42 154, 155 chemical shift tensors, 42 124 geometries, 42 135, 136 Isopropylcyclopentane, aromatization, 30 54 Isopropylcyclopropane, oxidation, 41 324 Isoteric enthalpy of adsorption, 38 154, 156 Isothermal heat of adsorption, 38 154, 158 Isotopes... 

Fig. 8. (a) MP2/6-311 + + G optimized geometry of the isopropyl cation with selected... 

Corma and co-workers152 have performed a detailed theoretical study (B3PW91/6-31G level) of the mechanism of the reactions between carbenium ions and alkanes (ethyl cation with ethane and propane and isopropyl cation with ethane, propane, and isopentane) including complete geometry optimization and characterization of the reactants, products, reaction intermediates, and transition states involved. Reaction enthalpies and activation energies for the various elemental steps and the equilibrium constants and reaction rate constants were also calculated. It was concluded that the interaction of a carbenium ion and an alkane always results in the formation of a carbonium cation, which is the intermediate not only in alkylation but also in other hydrocarbon transformations (hydride transfer, disproportionation, dehydrogenation). 

Asymmetric corner-protonated cyclopropane (55) and calculated geometry of classical isopropyl cation (56). (Structures reproduced from reference 229.)... 

Contrary to predictions from the CH acidities, deprotonation of phosphonium cations (i-Pr)n(cyciopropyl)4 P , which contain both isopropyl and cyclopropyl substituents, leads exclusively to ylides with the open-ehain isopropylide group.Evidently, the pyramidal carbanion geometry of cyclopropyhdes is much less favored than the planar carbanion geometry of iso-propylides. 

Among 2° carbocations, only the isopropyl, sec-butyl, and cyclopentyl carbocations have been observed in solution. These three structures nevertheless illustrate the kinds of delocalization effects that may be expected in other 2° carbocations. The cyclic structure of the cyclopentyl cation prevents significant C-C-C bridging. The calculated geometry (Figure 5.43) shows a twisted C2 structure with the C -H bonds aligned parallel with the empty p orbital for maximum hyperconjugative overlap. ... 

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