Hyperfine-Resolved Rotational Spectroscopy of Phenyl Radical

Changala, P. Bryan; McCarthy, Michael

doi:10.1021/acs.jpclett.3c01243

Cited by 3 publications

(3 citation statements)

References 71 publications

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“…It would be illuminating to extend this structural analysis to the 13 C and 17 O isotopologues of other species isoelectronic to propargyl and cyanomethyl, such as the ketenyl (OCCH) , and isocyanato (NCO) radicals. − These molecules are linear or quasilinear, with Renner–Teller-active 2 Π electronic states. − The high electronegativity of O should make OCCH • and • NCO the dominant resonance forms, which is a simple prediction to test with the electronic property information revealed by hyperfine analysis. Recent advances from our laboratory in the hyperfine-resolved rotational spectroscopy of aromatic and organometallic radicals demonstrate that exhaustive isotopic analysis has the potential to quantify the precise structural and electronic properties of even larger and more chemically diverse species. These types of studies will provide the vital physical insights needed to understand the pivotal role radicals play in the chemistry of atmospheric, combustion, and astrophysical environments.…”

Section: Discussionmentioning

confidence: 99%

Direct Probes of π-Delocalization in Prototypical Resonance-Stabilized Radicals: Hyperfine-Resolved Microwave Spectroscopy of Isotopic Propargyl and Cyanomethyl

Changala,

Franke,

Stanton

et al. 2024

J. Am. Chem. Soc.

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Delocalization of the unpaired electron in πconjugated radicals has profound implications for their chemistry, but direct and quantitative characterization of this electronic structure in isolated molecules remains challenging. We apply hyperfine-resolved microwave rotational spectroscopy to rigorously probe π-delocalization in propargyl, CH 2 CCH, a prototypical resonance-stabilized radical and key reactive intermediate. Using the spectroscopic constants derived from the high-resolution cavity Fourier transform microwave measurements of an exhaustive set of 13 C-and 2 H-substituted isotopologues, together with high-level ab initio calculations of zero-point vibrational effects, we derive its precise semiexperimental equilibrium geometry and quantitatively characterize the spatial distribution of its unpaired electron. Our results highlight the importance of considering both spin-polarization and orbital-following contributions when interpreting the isotropic hyperfine coupling constants of π radicals. These physical insights are strengthened by a parallel analysis of the isoelectronic species cyanomethyl, CH 2 CN, using new 13 C measurements also reported in this work. A detailed comparison of the structure and electronic properties of propargyl, cyanomethyl, and other closely related species allows us to correlate trends in their chemical bonding and electronic structure with critical changes in their reactivity and thermochemistry.

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Section: Discussionmentioning

confidence: 99%

Direct Probes of π-Delocalization in Prototypical Resonance-Stabilized Radicals: Hyperfine-Resolved Microwave Spectroscopy of Isotopic Propargyl and Cyanomethyl

Changala,

Franke,

Stanton

et al. 2024

J. Am. Chem. Soc.

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“…On the experimental side, radicals are unstable and reactive; thus, they are challenging species to be investigated and characterized. In this respect, quantum chemistry often plays a crucial role in providing accurate predictions and guidance in the interpretation of experiments. − …”

Section: Introductionmentioning

confidence: 99%

The Semiexperimental Approach at Work: Equilibrium Structure of Radical Species

Alessandrini,

Melosso,

Bizzocchi

et al. 2024

J. Phys. Chem. A

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The so-called semiexperimental (SE) approach is a powerful technique for obtaining highly accurate equilibrium structures for isolated systems. This Featured Article describes its extension to open-shell species, thus providing the first systematic investigation on radical equilibrium geometries to be used for benchmarking purposes. The small yet significant database obtained demonstrates that there is no reduction in accuracy when moving from closed-shell species to radicals. We also provide an extension of the applicability of the SE approach to medium-/ large-sized radicals by exploiting the so-called "Lego-brick" approach, which is based on the assumption that a molecular system can be seen as formed by smaller fragments for which the SE equilibrium structure is available. In this Featured Article we show that this model can be successfully applied also to open-shell species.

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“…One factor hindering its microwave detection at high spectral resolution is the complex splittings expected in its rotational spectrum as a result of the spin-rotation fine structure, which couples the electronic spin (S = 1/2) with the rotational angular momentum, and the nuclear magnetic hyperfine structure, which couples the hydrogen nuclear spins (I H = 1/2) with the electronic spin, similar to that observed in phenyl. 29 Indeed, although tentative evidence of the rotational spectrum of phenoxy was recently reported in our laboratory during the analysis of the products of a C 6 H 6 + O 2 electric discharge with broadband microwave spectroscopy, 30 no definitive assignments were attempted owing to the intricate, closely spaced line structure.…”

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confidence: 99%

Rotational Spectrum of the Phenoxy Radical

Changala,

McCarthy

2024

J. Phys. Chem. Lett.

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We report the hyperfine-resolved rotational spectrum of the gas-phase phenoxy radical in the 8−25 GHz frequency range using cavity Fourier transform microwave spectroscopy. A complete assignment of its complex but well-resolved fine and hyperfine splittings yielded a precisely determined set of rotational constants, spin-rotation parameters, and nuclear hyperfine coupling constants. These results are interpreted with support from high-level quantum chemical calculations to gain detailed insight into the distribution of the unpaired π electron in this prototypical resonance-stabilized radical. The accurate laboratory rest frequencies enable studies of the chemistry of phenoxy in both the laboratory and space. The prospects of extending the present experimental and theoretical techniques to investigate the rotational spectra of isotopic variants and structural isomers of phenoxy and other important gas-phase radical intermediates that are yet undetected at radio wavelengths are discussed.

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Hyperfine-Resolved Rotational Spectroscopy of Phenyl Radical

Cited by 3 publications

References 71 publications

Direct Probes of π-Delocalization in Prototypical Resonance-Stabilized Radicals: Hyperfine-Resolved Microwave Spectroscopy of Isotopic Propargyl and Cyanomethyl

Direct Probes of π-Delocalization in Prototypical Resonance-Stabilized Radicals: Hyperfine-Resolved Microwave Spectroscopy of Isotopic Propargyl and Cyanomethyl

The Semiexperimental Approach at Work: Equilibrium Structure of Radical Species

Rotational Spectrum of the Phenoxy Radical

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