A combined experimental and theoretical study is presented on the collision-induced dissociation (CID) of 9-methylguanine–1-methylcytosine base-pair radical cation (abbreviated as [9MG·1MC]˙ + ) and its monohydrate ([9MG·1MC]˙ + ·H 2 O) with Xe and Ar gases. Product ion mass spectra were measured as a function of collision energy using guided-ion beam tandem mass spectrometry, from which cross sections and threshold energies for various dissociation pathways were determined. Electronic structure calculations were performed at the DFT, RI-MP2 and DLPNO-CCSD(T) levels of theory to identify product structures and map out reaction potential energy surfaces. [9MG·1MC]˙ + has two structures: a conventional structure 9MG˙ + ·1MC (population 87%) consisting of hydrogen-bonded 9-methylguanine radical cation and neutral 1-methylcytosine, and a proton-transferred structure [9MG − H]˙·[1MC + H] + (less stable, population 13%) formed by intra-base-pair proton transfer from the N1 of 9MG˙ + to the N3 of 1MC within 9MG˙ + ·1MC. The two structures have similar dissociation energies but can be distinguished in that 9MG˙ + ·1MC dissociates into 9MG˙ + and 1MC whereas [9MG – H]˙·[1MC + H] + dissociates into neutral [9MG – H]˙ radical and protonated [1MC + H] + . An intriguing finding is that, in both Xe- andmore »
Electrocatalytic redox neutral [3 + 2] annulation of N -cyclopropylanilines and alkenes
Although synthetic organic electrochemistry (EC) has advanced significantly, net redox neutral electrosynthesis is quite rare. Two approaches have been employed to achieve this type of electrosynthesis. One relies on turnover of the product by the reactant in a chain mechanism. The other involves both oxidation on the anode and reduction on the cathode in which the radical cation or the radical anion of the product has to migrate between two electrodes. Herein, a home-built electrochemistry/mass spectrometry (EC/MS) platform was used to generate an N -cyclopropylaniline radical cation electrochemically and to monitor its reactivity toward alkenes by mass spectrometry (MS), which led to the discovery of a new redox neutral reaction of intermolecular [3 + 2] annulation of N -cyclopropylanilines and alkenes to provide an aniline-substituted 5-membered carbocycle via direct electrolysis (yield up to 81%). A chain mechanism, involving the regeneration of the substrate radical cation and the formation of the neutral product, is shown to be responsible for promoting such a redox neutral annulation reaction, as supported by experimental evidence of EC/MS.
- Award ID(s):
- 1915878
- Publication Date:
- NSF-PAR ID:
- 10275251
- Journal Name:
- Chemical Science
- Volume:
- 12
- Issue:
- 3
- Page Range or eLocation-ID:
- 969 to 975
- ISSN:
- 2041-6520
- Sponsoring Org:
- National Science Foundation
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- https://doi.org/10.1039/d0sc05665k
