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Issue 10, 2017
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Stabilization of carbocations CH3+, C2H5+, i-C3H7+, tert-Bu+, and cyclo-pentyl+ in solid phases: experimental data versus calculations

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Abstract

Comparison of experimental infrared (IR) spectra of the simplest carbocations (with the weakest carborane counterions in terms of basicity, CHB11Hal11, Hal = F, Cl) with their calculated IR spectra revealed that they are completely inconsistent, as previously reported for the t-Bu+ cation [Stoyanov E. S., et al. J. Phys. Chem. A, 2015, 119, 8619]. This means that the generally accepted explanation of hyperconjugative stabilization of the carbocations should be revised. According to the theory, one CH bond (denoted as Image ID:c6cp06839a-u1.gif) from each CH3/CH2 group transfers its σ-electron density to the empty 2pz orbital of the sp2 C atom, whereas the σ-electron density on the other CH bonds of the CH3/CH2 group slightly increases. From experimental IR spectra it follows that donation of the σ-electrons from the Image ID:c6cp06839a-u2.gif bond to the 2pz C-orbital is accompanied by equal withdrawal of the electron density from other CH bonds, that is, the electrons are supplied from each CH bond of the CH3/CH2 group. As a result, all CH stretches of the group are red shifted, and IR spectra show typical CH3/CH2 group vibrations. Experimental findings provided another clue to the electron distribution in the hydrocarbon cations and showed that the standard computational techniques do not allow researchers to explain a number of recently established features of the molecular state of hydrocarbon cations.

Graphical abstract: Stabilization of carbocations CH3+, C2H5+, i-C3H7+, tert-Bu+, and cyclo-pentyl+ in solid phases: experimental data versus calculations

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Publication details

The article was received on 06 Oct 2016, accepted on 07 Feb 2017 and first published on 13 Feb 2017


Article type: Paper
DOI: 10.1039/C6CP06839A
Phys. Chem. Chem. Phys., 2017,19, 7270-7279
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    Stabilization of carbocations CH3+, C2H5+, i-C3H7+, tert-Bu+, and cyclo-pentyl+ in solid phases: experimental data versus calculations

    E. S. Stoyanov and A. S. Nizovtsev, Phys. Chem. Chem. Phys., 2017, 19, 7270
    DOI: 10.1039/C6CP06839A

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