Original scientific paper

The C₃H₇+ Cation

Wolfram Koch ; Institut für Organische Chemie, Technische Universitàt Berlin, Strasse des 17. Juni 135, D-1000 Berlin 12, Germany
Paul von Rague Schleyer ; Institut für Organische Chemie, Universitàt Erlangen-Nürnberg, Henkestr. 42, D-8520 Erlangen, Germany
Peter Buzek ; Institut für Organische Chemie, Universitàt Erlangen-Nürnberg, Henkestr. 42, D-8520 Erlangen, Germany
Bowen Liu ; IBM Research Divison, Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099, U.S.A

Abstract

The C₃H₇+ potential energy surface (PES) is investigated using sophisticated ab initio quantum chemical calculations. All structures are fully optimized at the correlated MP2/6-311G(đ,p) level of theory. The C₃H₇+ potential energy surface is characterized by three classes of stationary points, corresponding to the 2-propyl cation, protonated cyclopropane and the 1-propyl cation. While for the first two species conformers representing minimum structures could be identified, no minimum was located for 1-propyl cation. Instead, the two 1-propyl cation structures are saddle points for carbon and of the hydrogen 2-propyl cation scrambling reactions . The global C₃H₇+ minimum is the chiral, C2-symmetric conformer of the 2-propyl cation, which lies 7.2 kcal/mol below the second C₃H₇+ minimum, i.e. asymmetrically corner-protonated cyclopropane. In both species, methyl rotation is practically free. The two 1-propyl-cation like saddle points are 19.3 and 20.5 kcal/mol above the global minimum. By comparison of the theoretical and experimental 13C-NMR and IR spectra of 2-propyl cation, the C2-symmetric structure is identified as the structure present in solution. The preference of the unexpected, twisted geometry of this cation can be attributed to stabilizing hyperconjugation. The proton affinities and heats of formation of the various C₃H₇+ species are computed and compared to the experimental data.

Keywords

Hrčak ID:

137124

URI

https://hrcak.srce.hr/137124

Publication date:

15.10.1992.

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