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Tuning the Ground State Symmetry of Acetylenyl Radicals.

ABSTRACT: The lowest excited state of the acetylenyl radical, HCC, is a (2)? state, only 0.46 eV above the ground state, (2)?(+). The promotion of an electron from a ? bond pair to a singly occupied ? hybrid orbital is all that is involved, and so we set out to tune those orbital energies, and with them the relative energetics of (2)? and (2)?(+) states. A strategy of varying ligand electronegativity, employed in a previous study on substituted carbynes, RC, was useful, but proved more difficult to apply for substituted acetylenyl radicals, RCC. However, ?-donor/acceptor substitution is effective in modifying the state energies. We are able to design molecules with (2)? ground states (NaOCC, H2NCC ((2)A?), HCSi, FCSi, etc.) and vary the (2)?(+)-(2)? energy gap over a 4 eV range. We find an inconsistency between bond order and bond dissociation energy measures of the bond strength in the Si-containing molecules; we provide an explanation through an analysis of the relevant potential energy curves.

SUBMITTER: Zeng T

PROVIDER: S-EPMC4827494 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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Tuning the Ground State Symmetry of Acetylenyl Radicals.

Zeng Tao T Danovich David D Shaik Sason S Ananth Nandini N Hoffmann Roald R

ACS central science 20150811 5

The lowest excited state of the acetylenyl radical, HCC, is a (2)Π state, only 0.46 eV above the ground state, (2)Σ(+). The promotion of an electron from a π bond pair to a singly occupied σ hybrid orbital is all that is involved, and so we set out to tune those orbital energies, and with them the relative energetics of (2)Π and (2)Σ(+) states. A strategy of varying ligand electronegativity, employed in a previous study on substituted carbynes, RC, was useful, but proved more difficult to apply ...[more]

PMID: 27162981

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