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Updated: Sep 27, 2025

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Can a gas phase contact ion pair containing a hydrocarbon carbocation be formed in the ground state?
José R Araújo1, Railton B de Andrade1, Hélcio J Batista2
1Departamento de Química, CCEN, Universidade Federal da Paraíba João Pessoa PB 58059-900 Brazil silmar@quimica.ufpb.br.
Abstract:
So far, no conclusive evidence of a ground-state contact ion-pair containing a hydrocarbon carbocation has been given in the gas phase. Due to the very high stability of the 1,2:4,5-dibenzotropylium (or dibenzo[a,d]tropylium) carbocation, we suggest (supported by DFT and MP2 calculations) the formation of a contact ion pair between this carbocation and chloride, occurring during the reaction between 1,2:4,5-dibenzotropyl (also named dibenzo[a,d]tropyl or dibenzo[a,d]cycloheptenyl) radical and chlorine atom at very low temperatures, through the harpoon mechanism. This is the first modeling study to find computational evidence for the possibility of a gas-phase contact ion pair (containing a hydrocarbon carbocation) formed in the ground state. Identification of this metastable species can be carried out by trapping it in He nanodroplets, along with infrared laser spectroscopy routinely coupled with this technique.
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