Quantum-mechanical calculations of the stabilities of fluxional isomers of C 4 H\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}\begin{equation*}{\mathrm{_{7}^{+}}}\end{equation*}\end{document} in solution

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Abstract
Although numerous quantum calculations have been made over the years of the stabilities of the fluxional isomers of C4H , none have been reported for other than the gas phase (which is unrealistic for these ionic species) that exhibit exceptional fluxional properties in solution. To be sure, quantum-mechanical calculations for solutions are subject to substantial uncertainties, but nonetheless it is important to see whether the trends seen for the gas-phase C4H species are also found in calculations for polar solutions. Of the C4H species, commonly designated bisected-cyclopropylcarbinyl 1, unsym-bicyclobutonium 2, sym-bicyclobutonium 3, allylcarbinyl 4, and pyramidal structure 6, the most advanced gas-phase calculations available thus far suggest that the order of stability is 1 ≥ 2 ≥ 3 ≫ 4 ≫ 6 with barriers of only ≈1 kcal/mol for interconversions among 1, 2, and 3. We report here that, when account is taken of solvation, 2 turns out to be slightly more stable than 1 or 3 in polar solvents. The pattern of the overall results is unexpected, in that despite substantial differences in structures and charge distributions between the primary players in the C4H equilibria and the large differences in solvation energies calculated for the solvents considered, the differential solvent effects from species to species are rather small.

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