preprints.org > chemistry and materials science > theoretical chemistry > doi: 10.20944/preprints202407.0102.v1 (registering DOI)

Preprint Article Version 1 This version is not peer-reviewed

Version 1 : Received: 1 July 2024 / Approved: 1 July 2024 / Online: 1 July 2024 (12:57:10 CEST)

Oxidation of a mixture of nonlabelled (14N2H4) and 15N labeled (15N2H4) hydrazine in aqueous solutions produces 14N15N molecules, indicating the intermediate existence of N4H6 or N4H4 dimers with subsequent transfers of H atoms and splitting of lateral N-N bonds. To explain the key part of hydrazine oxidation reaction, the structures, thermodynamics, and electron characteristics of N4H4 molecules in aqueous solution are investigated at CCSD/cc-pVTZ level of theory. We have not found any spontaneous splitting of the bond between lateral nitrogen atoms in tetrazenes N4H4 during geometry optimization. The most probable N4H4 oxidation products are H2N-NH2 and N2, which are obtained by splitting the bond between central nitrogen atoms and so only 15N2 and 14N2 molecules are formed. Additionally, the formation of H3N-NH and N2 oxidation products is also preferred to structures without any N-N fissions. The formation of H2N=N and HN=NH reaction products is energetically less advantageous. Cyclo-N4H4 structures are stable, without any N-N fissions, but their very high Gibbs energies indicate their vanishing abundance in aqueous solution, so their involvement in hydrazine oxidation is highly improbable. Hydrazine oxidation to 14N15N molecules cannot be explained by tetrazene N4H4 intermediates.

Coupled Cluster; geometry optimization; N-N bond fission; QTAIM analysis; electron structure

Chemistry and Materials Science, Theoretical Chemistry

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