Isobutane geometry

Superacid-catalyzed alkylation of adamantane with lower alkenes (ethene, propene, isomeric butenes) has been investigated by Olah et al.151 in triflic acid and triflic acid-B(0S02CF3)3. Only trace amounts of 1 -ferf-butyladamantane (37) were detected in alkylation with 1- and 2-butenes, whereas isobutylene gave consistently relatively good yield of 37. Since isomerization of isomeric 1-butyladamantane under identical conditions did not give even traces of 37, its formation can be accounted for by (r-alkylation, that is, through the insertion of the ferf-butyl cation into the C—H bond (Scheme 5.22). This reaction is similar to that between ferf-butyl cation and isobutane to form 2,2,3,3-tetramethylbutane discussed above (Scheme 5.21). In either case, the pentacoordinate carbocation intermedate, which may also lead to hydride transfer, does not attain a linear geometry, despite the unfavorable steric interactions. 

Intermolecular hydride transfers between t-alkyl centres are observed under stable ion solution conditions. These have very low activation enthalpies (Dirda et al., 1979) and accurate rate data are scarce. The simplest reaction, transfer from isobutane to the t-butyl cation in sulphur dioxide, has been shown to be first order in each component, and to have Ea = 15.1 kJ mol 1 and AS = — lBJK moP1 (Brownstein and Bornais, 1971). Adaman-tane catalyses solution hydride transfer between acyclic tertiary centres such as t-butyl, and it is believed that this reflects higher efficiency of hydride transfers to and from bridgehead 1-adamantyl cation. With its non-planar geometry, the non-bonded interactions between alkyl substituents on donor and acceptor are likely to be less than those between two acyclic reactants. If locking of rotation about the C- H- C axis between the reactants does not... 

H-abstraction reactions occur preferably on tertiary carbon centers. Therefore isobutane is a good candidate for studying this reaction channel. The geometry of the adsorbed complex, as well as that of the transition structure (Rg. 13) is qualitatively similar to the structures found by Milan and... 

It can be shown that the frequency, where the out-of-phase characteristic FR Figure 6. The temperature dependence of the, ction of diffusion is a maximum, isobutane diffusivity (D) in the micropores of H- j e particle geometry [7, 8]. 

The epoxide is used as a monomer for polymer production. The byproduct ethylbenzene alcohol can be dehydrated to styrene, also a monomer for the production of polymers. If isobutane is used, iso-butylhydroperoxide replaces ethylbenzene-hydroperoxide as the oxidant. The byproduct tert-butanol can be converted with methanol to an ether that is an important additive in new environmental friendly gasolines. Complexes of Mo, V, or Ti are used in homogeneous epoxidation catalysis, while heterogeneous Ti02/Si02 catalysts can be used also. The active sites consist of a titanium ion with a fourfold coordination of oxygen in a tetrahedral geometry. Titanium acts essentially as a Lewis acid to activate the 0-0 bond in the hydroperoxide. 

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