Alkonium ions

A comparison of C—C and C—H bond reactivities in protolytic reactions indicated that under the conditions of alkylation C—H cleavage is much more pronounced (in the reaction of ethane, the relative ratio of C—C C—H cleavages is 9 1 in the absence of benzene and 1 10 in the presence of benzene). This indicates that overall alkylation can also involve the attack of protonated benzene (benzenium ion) on the C—H bond of the alkane [Eq. (5.48)] or interaction of benzene with the five-coordinate alkonium ion prior to its cleavage to the trivalent cation ... 

Protonated alkanes (C H2 , 3 ) also play a significant role in alkane reactions. Saturated hydrocarbons can be protonated to alkonium ions, of which the methonium ion CH5+, 422 [Eq. (3.119)] is the parent, and formation of these pentacoordinate carbocations involves two-electron three-center (2e—ic) bonds. The dotted lines in the structure symbolize the bonding orbitals of the three-center bonds [Eq. (3.119)] their point of junction does not represent an additional atom. 

Alkonium Ions Incorporating Bridging Hydrogens (Protonated... 

Proponium Ions and Analogs The higher alkonium ions, such as protonated propane (C3H9+) [and also protonated butane (C4H1T), etc.], have been observed in the gas phase by In solution, the higher hydrocar-... 

I.6. Higher Alkonium Ions The acid-induced H-D exchange of isobutane (49) in deuterosulfuric acid was studied by Otvos and coworkers. All nine methyl hydrogens were readily exchanged, but not the methine hydrogen. The mechanism for this observation is considered to involve the initial formation of trivalent zerz-butyl cation (50), probably in an oxidative... 

The formation of the Pt(II)-alkane complex as the first kinetically significant intermediate in the reaction has been proposed in the so called alkane-alkyl mechanism (see above) [14], This intermediate is analogous to alkonium ions of the type CHs whose formation is associated with the deformation of both the planar complex and of the tetrahedral hydrocarbon molecule. 

Protonated saturated hydrocarbons contain a carbon atom which is formally 5-coordinate. There are insufficient electrons to describe such a carbocation by a classical structure and it is necessary to invoke a 3-centre 2-electron bond. This family of non-classical alkonium ions are generally known as carbonium ions. Removal of H2 from an alkonium ion leaves a carbocation containing a 3-coordinate carbon. These trivalent alkyl cations are known as carbenium ions. The interrelation between the two classes of carbocations is shown for the parent ions in equation 2. 

Higher alkonium ions. Hiraoka and Kebarle also examined the next two homologues of the alkonium ions, 3119 and C4H11 . As in there is the possibility of either... 

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