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Quantum-mechanical calculations of the stabilities of fluxional isomers of C_4H_7^+ in solution

Casanova, Joseph and Kent, David R., IV and Goddard, William A., III and Roberts, John D. (2003) Quantum-mechanical calculations of the stabilities of fluxional isomers of C_4H_7^+ in solution. Proceedings of the National Academy of Sciences of the United States of America, 100 (1). pp. 15-19. ISSN 0027-8424. PMCID PMC140868.

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Although numerous quantum calculations have been made over the years of the stabilities of the fluxional isomers of C4H7+, 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 C4H7+ species are also found in calculations for polar solutions. Of the C4H7+ 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 C4H7+ 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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Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2003 by the National Academy of Sciences. Contributed by John D. Roberts, November 8, 2002. Published online before print December 30, 2002, 10.1073/pnas.0136820100 We acknowledge the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. We are also deeply indebted to the Summer Undergraduate Research Fellowship Program (SURF), Dr. and Mrs. Chester M. McCloskey, and The Camille and Henry Dreyfus Foundation for their helpful financial assistance. D.R.K. is grateful for a graduate fellowship from The Fannie and John Hertz Foundation. The quantum chemistry calculations reported here were funded by Department of Energy Accelerated Strategic Computational Initiative (DOE/ASCI-ASAP W-7405-ENG-48). The computational facilities were funded in part by the National Science Foundation (CHE-9977872) and the Army Research Office (Defense University Research Instrumentation Program).
Funding AgencyGrant Number
American Chemical Society Petroleum Research FundUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Dr. and Mrs. Chester M. McCloskeyUNSPECIFIED
Camille and Henry Dreyfus FoundationUNSPECIFIED
Fannie and John Hertz FoundationUNSPECIFIED
Department of Energy (DOE)W-7405-ENG-48
Army Research Office (ARO)UNSPECIFIED
Subject Keywords:nuclear-magnetic-resonance, interconversion, energies, spectra, cation, ions
Issue or Number:1
PubMed Central ID:PMC140868
Record Number:CaltechAUTHORS:CASpnas03
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1294
Deposited By: Tony Diaz
Deposited On:09 Jan 2006
Last Modified:02 Oct 2019 22:42

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