Diprotonated methane

With Lammerstma and Simonetta in 1982, we studied the parent six-coordinate diprotonated methane (CH/ ), which has two 2e-3c bonding interactions in its minimum-energy structure (Cid- On the basis of ab initio calculations, with Rasul we more recently found that the seven-coordinate triprotonated methane (CHy ) is also an energy minimum and has three 2e-3c bonding interactions in its minimum-energy structure 3 ). These results indicate the general importance of 2e-3c bonding in protonated alkanes. 

Carbon can not only be involved in a single two-electron three-center bond formation but also in some carbodications simultaneously participate in two 2e-3c bonds. Diprotonated methane (CH/ ) and ethane... 

For the CH with a Cs symmetrical structure 1 a 13C NMR chemical shift of 11.5 ppm is calculated. This is 7.1 ppm more shielded than that calculated for the hydrocarbon CH4 at the GIAO-MP2 level.19 The shielding effect in 1 is as expected for a hypercoordinated carbocation carbon.20 The calculated minimum energy structure for diprotonated methane (CHi+) 2 has C2v symmetry with two 3c-2e... 

Protonated carbonic acid (fFCCF-1-, 175) is recognized as a stable species in superacids and even a salt was isolated with its X-ray crystal structure obtained. In strong superacids, diprotonated carbonic acid (30) was found to undergo ionic hydrogenation to methane (eq 45).77... 

Multiply-Protonated Methane Ions and their Analogs In addition to the involvement in a single 3c-2e bond formation, carbon is also capable of simultaneously participating in two 3c-2e bonds in some carbodications. Diprotonated methane (protiomethonium dication, C l P ) is the parent of such carbodications. 

Quantum mechanical calculations (by ab initio method) "" performed on diprotonated methane showed that the symmetrical structure (18) with two stabilizing orthogonal 3c-2e interactions is the only minimum on the potential energy surface. The other structures (19-22), in turn, were calculated to be saddle points on the potential energy surface. These were found to be... 

Using the GIAO-MP2 method (tzp/dz basis set), Rasul et aU " calculated the B NMR chemical shifts of hypercoordinate boron atoms in selected boron compounds and NMR chemical shifts of the corresponding isoelectronic and isostructural carbocations for systems not yet observed under long-lived superacidic conditions B NMR and NMR chemical shift values for the methonium ion CH5+ (5) and the corresponding neutral boron analog BHs (15) were shown to reproduce well the experimental values. Calculations were also performed for the six-coordinate carbocation (diprotonated methane, 18) seven-coordinate carbocation (triprotonated methane, 27) the... 

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