THREE UNT CHEMISTRY GRADUATE STUDENTS WIN AWARDS AT RMRM2020 | Department of Chemistry

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December 1, 2020

THREE UNT CHEMISTRY GRADUATE STUDENTS WIN AWARDS AT RMRM2020

Congratulations to three Chemistry graduate students for winning Flash Presentation Awards at the virtual Rocky Mountain Regional Meeting 2020 (RMRM2020), November 12-13, 2020.

  • Waad Alharbi (Cundari Group) won one of 3 Elsevier Coordination Chemistry Awards for her presentation: C-H activation of toluene by diruthenium nitride: DFT study
    • Abstract: Two diruthenium-azide species are modelled to investigate nitrogen insertion into a C-H bond of toluene. Model 1 has four formate bridging ligands; Model 2 is larger and has benzoate bridging ligands. For each of these, three different mechanisms were studied. The first two mechanisms - amination - are achieved via hydrogen atom abstraction (HAA) of either a benzylic (sp3) C-H or an aromatic (sp2) C-H bond of toluene, followed by radical rebound (RR), yielding a new Csp3-N (benzylamine) or Csp2-N bond (para-toluidine), respectively. The third route studied - nitrene addition - first forms an aziridine-like intermediate, which is followed by a hydrogen transfer to produce the same Csp2-N bond para-toluidine as the sp2 C-H amination route. Toluene's reactivity with Ru2N intermediates was accomplished from analysis of geometric features and free energy calculations and shows that a benzylic C-H amination via HAA/RR route is the most favorable route kinetically among the three activation pathways studied.
  • Carly Carter (Cundari Group) won the Inorganics Division Award for her presentation: Olefin polymerization by zirconium boratabenzene catalystst
    • Abstract: In the present quantum chemical study, α-olefin dimerization and trimerization by zirconium boratabenzene catalysts has been studied as the single site reactivity of Group 4 metallocene catalysts has proven to be industrially important. The thermodynamics and kinetics of C=C insertion for ethylene, 1- butene, and 1-hexene as well as relevant β-H elimination barriers have been quantified using density functional theory, using methodology previously calibrated in earlier research by the UNT and EMCC team for bis-indenyl zirconium catalysts. The insertions of the alkenes are relevant to chain growth processes, while the β-H eliminations model chain termination. Various substituents on the boratabenzene rings were also compared to determine how these ligands change the behavior of the thermodynamics and kinetics of the insertion and chain termination steps.
  • Ramesh Sapkota (Marshall Group) won the ACS Sustainability Award for his presentation: Infrared spectrum and atmospheric chemistry of 1,1,2,3,3,4,4 heptafluorobut-1-ene
    • Abstract: The recognition that photolysis of hydrochlorofluorocarbon (HCFC) compounds depletes stratospheric ozone has led to their substitution by hydrofluorocarbon (HFC) compounds. However, such species absorb infrared radiation strongly and, if this is coupled to a long atmospheric lifetime, HFCs can exhibit high global warming potentials (GWP). Here we characterize a fluorinated alkene which, by virtue of the pi bond, offers the chance for high reactivity with atmospheric radicals and thus a small lifetime and GWP. The relative rate method was used to determine the reaction rate of heptafluorobut-1-ene (CF2=CFCF2CF2H) with chlorine atoms. A mercury UV lamp photolyzed Cl2 and the reaction was monitored by FTIR spectroscopy. Ethane was the reference compound for relative rate studies. The rate constant was found to be (3.8 ± 0.4) 10-11 cm3 molecule-1 s-1 in 750 torr of argon diluent at 296 K. With 25% added O2, oxidation of heptafluoro-but-1-ene initiated by a chlorine atom creates carbonyl difluoride (COF2) with 95 ± 7 % yield and 2,2,3,3 tetrafluoro-propanoyl fluoride (O=CFCF2CF2H) as the only other product. The IR cross-sections of heptafluoro-but-1-ene yield a radiative efficiency of 0.29 W m-2 ppb-1 and its GWP was calculated to be 0.08 for 100 years' time horizon. Subtracting a reference COF2 spectrum from the oxidative product spectrum we obtain the first IR spectrum of 2,2,3,3 tetrafluoropropanoyl fluoride. Its radiative efficiency is 0.18 W m-2 ppb-1 and its GWP is 0.05 for 100 years' time horizon. Anharmonic frequency calculations for 1,1,2,3,3,4,4 heptafluorobut-1-ene and 2,2,3,3 tetrafluoropropanoyl fluoride based on density functional theory (B2PLYP/N07D) are in good accord with measurements, when all low-energy conformations are taken into account.

You may view a list of all the RMRM 2020 awards, including the Flash Presentation Awards, here.