From Molecules with a Planar Tetracoordinate Carbon to an Astronomically Known C5H2 Carbene

Amir Karton; Venkatesan S Thimmakondu

doi:10.1021/acs.jpca.2c01261

From Molecules with a Planar Tetracoordinate Carbon to an Astronomically Known C₅H₂ Carbene

J Phys Chem A. 2022 Apr 28;126(16):2561-2568. doi: 10.1021/acs.jpca.2c01261. Epub 2022 Apr 15.

Authors

Amir Karton¹, Venkatesan S Thimmakondu²

Affiliations

¹ School of Molecular Sciences, The University of Western Australia, Perth, Western Australia 6009, Australia.
² Department of Chemistry and Biochemistry, San Diego State University, San Diego, California 92182-1030, USA.

Abstract

Ethynylcyclopropenylidene (2), an isomer of C₅H₂, is a known molecule in the laboratory and has recently been identified in Taurus Molecular Cloud-1 (TMC-1). Using high-level coupled-cluster methods up to the CCSDT(Q)/CBS level of theory, it is shown that two isomers of C₅H₂ with a planar tetracoordinate carbon (ptC) atom, (SP-4)-spiro[2.2]pent-1,4-dien-1,4-diyl (11) and (SP-4)-spiro[2.2]pent-1,4-dien-1,5-diyl (13), serve as the reactive intermediates for the formation of 2. Here, a theoretical connection has been established between molecules containing ptC atoms (11 and 13) and a molecule (2) that is present nearly 430 light years away, thus providing evidence for the existence of ptC species in the interstellar medium. The reaction pathways connecting the transition states and the reactants and products have been confirmed by intrinsic reaction coordinate calculations at the CCSDT(Q)/CBS//B3LYP-D3BJ/cc-pVTZ level. While isomer 11 is non-polar (μ = 0), isomers 2 and 13 are polar, with dipole moment values of 3.52 and 5.17 Debye at the CCSD(T)/cc-pVTZ level. Therefore, 13 is also a suitable candidate for both laboratory and radioastronomical studies.