Aromatic Stabilization and Hybridization Trends in Photoelectron Imaging of Heterocyclic Radicals and Anions

Lori M. Culberson, Christopher C. Blackstone, Adam A. Wallace, Andrei Sanov

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10 Scopus citations

Abstract

We examine the photoelectron spectra and laboratory-frame angular distributions in the photodetachment of furanide (C4H3O-), thiophenide (C4H3S-), and thiazolide (C3H2NS-) and compare the results to the previously reported studies of pyridinide (C5H4N-) and oxazolide (C3H2NO-). Using the mixed s-p model for the angular distributions, the results are interpreted in terms of the effective fractional p character of the highest-occupied molecular orbitals of these heterocyclic anions, revealing trends related to the aromaticity. We conclude that aromatic stabilization across a series of systems may be tracked using the photoelectron angular distributions. In addition, we report an improved (higher-precision) electron affinity (EA) for the thiophenyl radical, EA(C4H3S) = 2.089(8) eV. The EA of thiazolyl falls within the 2.5(1) eV range, but it is not clear if this determination corresponds to the 2- or 5-cyclic species or the 2-ring-open isomer. These results are analyzed in conjunction with the properties of other heterocyclic radicals (pyridinyl, furanyl, and oxazolyl) and interpreted in terms of the C-H bond dissociation energies (BDEs) of the corresponding closed-shell molecules. The BDEs of all five-membered-ring heterocyclics studied fall within the 116-120 kcal/mol range, contrasting the lower BDE = 110.4(2.0) kcal/mol of the more aromatic six-membered-ring pyridine. The observed aromaticity trends are consistent with the findings derived from the anion photoelectron angular distributions.

Original languageEnglish (US)
Pages (from-to)9770-9777
Number of pages8
JournalJournal of Physical Chemistry A
Volume119
Issue number38
DOIs
StatePublished - Sep 24 2015

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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