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1. Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν 3 / ν 4 CH stretch modes and CH 2 internal rotor dynamics of benzyl radical

   https://doi.org/10.1039/c7cp05776h  

   Kortyna, A. ; Samin, A. J. ; Miller, T. A. ; Nesbitt, D. J. ( January 2017 , Physical Chemistry Chemical Physics)

   Highly reactive benzyl radicals are generated by electron dissociative attachment to benzyl chloride doped into a neon–hydrogen–helium discharge and immediately cooled to T rot = 15 K in a high density, supersonic slit expansion environment. The sub-Doppler spectra are fit to an asymmetric-top rotational Hamiltonian, thereby yielding spectroscopic constants for the ground ( v = 0) and first excited ( v = 1, ν 3 , ν 4 ) vibrational levels of the ground electronic state. The rotational constants obtained for the ground state are in good agreement with previous laser induced fluorescence measurements (LIF), with vibrational band origins ( ν 3 = 3073.2350 ± 0.0006 cm −1 , ν 4 = 3067.0576 ± 0.0006 cm −1 ) in agreement with anharmonically corrected density functional theory calculations. To assist in detection of benzyl radical in the interstellar medium, we have also significantly improved the precision of the ground state rotational constants through combined analysis of the ground state IR and LIF combination differences. Of dynamical interest, there is no evidence in the sub-Doppler spectra for tunneling splittings due to internal rotation of the CH 2 methylene subunit, which implies a significant rotational barrier consistent with partial double bond character in the CC bond. This is further confirmed with high level ab initio calculations at the CCSD(T)-f12b/ccpVdZ-f12 level, which predict a zero-point energy corrected barrier to internal rotation of Δ E tun ≈ 11.45 kcal mol −1 or 4005 cm −1 . In summary, the high-resolution infrared spectra are in excellent agreement with simple physical organic chemistry pictures of a strongly resonance-stabilized benzyl radical with a nearly rigid planar structure due to electron delocalization around the aromatic ring. 

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2. H 2 O 2 and CH 3 OOH (MHP) in the Remote Atmosphere: 2. Physical and Chemical Controls

   https://doi.org/10.1029/2021JD035702  

   Allen, Hannah M. ; Bates, Kelvin H. ; Crounse, John D. ; Kim, Michelle J. ; Teng, Alexander P. ; Ray, Eric A. ; Wennberg, Paul O. ( March 2022 , Journal of Geophysical Research: Atmospheres)

   Hydrogen peroxide (H₂O₂) and methyl hydroperoxide (MHP, CH₃OOH) serve as HO_x(OH and HO₂radicals) reservoirs and therefore as useful tracers of HO_xchemistry. Both hydroperoxides were measured during the 2016–2018 Atmospheric Tomography Mission as part of a global survey of the remote troposphere over the Pacific and Atlantic Ocean basins conducted using the NASA DC‐8 aircraft. To assess the relative contributions of chemical and physical processes to the global hydroperoxide budget and their impact on atmospheric oxidation potential, we compare the observations with two models, a diurnal steady‐state photochemical box model and the global chemical transport model Goddard Earth Observing System (GEOS)‐Chem. We find that the models systematically under‐predict H₂O₂by 5%–20% and over‐predict MHP by 40%–50% relative to measurements. In the marine boundary layer, over‐predictions of H₂O₂in a photochemical box model are used to estimate H₂O₂boundary‐layer mean deposition velocities of 1.0–1.32 cm s⁻¹, depending on season; this process contributes to up to 5%–10% of HO_xloss in this region. In the upper troposphere and lower stratosphere, MHP is under‐predicted and H₂O₂is over‐predicted by a factor of 2–3 on average. The differences between the observations and predictions are associated with recent convection: MHP is under‐estimated and H₂O₂is over‐estimated in air parcels that have experienced recent convective influence.

    

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3. Computer‐Assisted 3D Structure Elucidation (CASE‐3D): The Structural Value of 2 J CH in Addition to 3 J CH Coupling Constants

   https://doi.org/10.1002/anie.201915103  

   Koos, Martin R. M. ; Navarro‐Vázquez, Armando ; Anklin, Clemens ; Gil, Roberto R. ( January 2020 , Angewandte Chemie International Edition)

   We present a method to use long‐range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 79²J_CHand³J_CHvalues collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE‐3D (computer‐assisted 3D structure elucidation) protocol. In addition to the most commonly used³J_CHcoupling constants, the subset of 32²J_CHvalues alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT‐calculated^2,3J_CHvalues with experimental ones, critical for the case of²J_CH. But the configuration selection also works well using³J_CHvalues predicted from a semi‐empirical Karplus‐based equation limited to H−C−C−C fragments. The robustness, shown using strychnine as a proof of concept, makes theJ‐based CASE‐3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural‐product identification and analysis, as well as medicinal chemistry.

    

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4. Computer‐Assisted 3D Structure Elucidation (CASE‐3D): The Structural Value of 2 J CH in Addition to 3 J CH Coupling Constants

   https://doi.org/10.1002/ange.201915103  

   Koos, Martin R. M. ; Navarro‐Vázquez, Armando ; Anklin, Clemens ; Gil, Roberto R. ( January 2020 , Angewandte Chemie)

   We present a method to use long‐range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 79²J_CHand³J_CHvalues collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE‐3D (computer‐assisted 3D structure elucidation) protocol. In addition to the most commonly used³J_CHcoupling constants, the subset of 32²J_CHvalues alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT‐calculated^2,3J_CHvalues with experimental ones, critical for the case of²J_CH. But the configuration selection also works well using³J_CHvalues predicted from a semi‐empirical Karplus‐based equation limited to H−C−C−C fragments. The robustness, shown using strychnine as a proof of concept, makes theJ‐based CASE‐3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural‐product identification and analysis, as well as medicinal chemistry.

    

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5. Disproportionation of Sn(II){CH(SiMe 3 ) 2 } 2 to ·Sn(III){CH(SiMe 3 ) 2 } 3 and ·Sn(I){CH(SiMe 3 ) 2 }: Characterization of the Sn(I) Product

   https://doi.org/10.1039/d3cc01542d  

   Mears, Kristian ; Nguyen, Gia-Ann ; Ruiz, Bronson ; Zou, Wenxing ; Fettinger, James C ; Power, Philip P ( May 2023 , Chemical Communications)

   Half a century since the photocatalytic disproportionation of Lappert's dialkyl stannylene SnR 2 , R = CH(SiMe 3 ) 2 (1) gave the persistent trivalent radical [·SnR 3 ], the characterization of the corresponding Sn(I) product, ·SnR is now described. It was isolated as the hexastannaprismane Sn 6 R 6 (2), from the reduction of 1 by the Mg(I)-reagent, Mg(BDI Dip ) 2 , (BDI = (DipNCMe) 2 CH, Dip + 2,6-diisopropylphenyl). 

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