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Goodlinear correlations between GIAO–CCSD(T) calculated 11B NMR chemical shifts of hypercoordinate boronium 1–6band borenium 7–9bionsand 13C NMR chemical shifts of the correspondingisoelectronic carbonium 1–6aandcarbenium 7–9aions, respectively,were found. [ABSTRACT FROM AUTHOR]

The carbonium ion has been suggested to be the intermediateinsuperacid-promoted reactions (SbF5–HF) such as hydrogen–deuteriumexchange and in the electrophilic C–H cleavage into hydrogenand the carbenium ion. In this study, the superacid-promoted C–Hcleavage into hydrogen and the carbenium ion was studied using densityfunctional theory (B3LYP and M062X) and ab initio methods (MP2 andCCSD). The calculations suggest that the superacid-promoted C–Hcleavage proceeds via a concerted transition state leading to hydrogen(H2) and the carbenium ion without the formation of theelusive carbonium ion. The reactivity for the superacid-promoted C–Hcleavage decreases upon going from isobutane (tertiary) > propane(secondary) > isobutane (primary) > propane (primary) > ethane≫methane. [ABSTRACT FROM AUTHOR]

Nonclassical ions or carbonium ions have multi-center bonding from delocalized or electrons. The 2-norbornyl cation, its derivative 6,6-difluoro-2-norbornyl cation, tris-homocyclopropenyl cation, 7-norbornenyl cation, and 4-cyclopentenyl cation and their corresponding silicon analogues were studied in this work. All carbocations have topologically different 3c−2e systems. The magnitude of all delocalization indexes between each atomic pair of the 3c−2e bond can be used to predict homoaromaticity. The silicon analogues have a topologically different 3c−2e bond from their corresponding carbocation. [ABSTRACT FROM AUTHOR]

Computed B3LYP/6-31G(d,p) and MP2/6-31G(d,p) structures and binding energies for complexes of nonclassical cations (carbonium ions) with ammonia, in the gas phase and several solvents, are described. Overall, nonclassical cations are found to be competent C−H hydrogen bond donors. The potential relevance of the C−H···N interactions holding the carbocation·amine complexes together for enzyme-catalyzed terpenoid synthesis is discussed. [ABSTRACT FROM AUTHOR]

C7H122+ (1), the prototype hexacoordinate carbonium dication was found to be a viable minimum at the MP2/6-31G** and MP2/cc-pVTZ levels. Structure 1 is a propeller shaped molecule resembling a complex involving a C2+ with three ethylene molecules resulting in the formation of three two-electron, three-center (2e-3c) bonds. Isomeric structure 2 was found to be 21.8 kcal/mol more stable than structure 1. However, conversion of 1 into 2 through transition structure 3 has a barrier of 5.7 kcal/mol. Related structures 4,5, and 8 were also located as minima for C7H122+. The isoelectronic boron analogue BC6H12+ (10) was also computed to be a minimum at the same level of calculations. [ABSTRACT FROM AUTHOR]