Hypercoordinate Carbocations Containing

The CH cation 1, protonated methane, is the parent of hypercoordinated carbocations containing a five coordinated carbon atom. It is elusive in solution and has not been observed by NMR spectroscopy but gas-phase infrared investigations have shown its fluxional structure which has been proven by ab initio molecular dynamic simulation.18... 

The second class of carbocations contains one or more hypercoordinate carbon atoms. These hypercarbons are coordinated to five or more atoms within reasonable bonding distance. Hypercoordinate or nonclassical carbocations cannot be described by using 2c-2e single bonds alone, but necessitate the involvement of three- (or multi-) center, two-electron bonds, e.g., 3c-2e bonds. Each hypercarbon in the cation is always associated with eight electrons, although the ion, overall, is electron deficient. The methonium ion (Cd I5 ) may be considered the parent of the hypercoordinate carbocations (Fig. 5.1). 

The hydrogen-bridged carbocation (B) contains a two-coordinate hydrogen atom. Hypercoordination— which includes two-coordination for hydrogen and at least five-coordination for carbon—is generally... 

To illustrate the wide and developing scope of hypercarbon chemistry by illustrating the variety of compounds now known to contain hypercarbon atoms (carbocations,organometallics, carboranes, metal-carbon cluster compounds," and metal carbides ).They include bridged metal alkyls such as alkyl-lithium reagents (LiR) in which the hypercoordinated nature of the metal-attached carbon atoms, and the roles that the metal atoms play in their chemistry, are often overlooked. 

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