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Browsing by Author "Kelley, Sarah Ariel"

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    Nitrosoarenes: magnetic anisotropy, donor-acceptor bonding and host-guest chemistry
    (University of Alabama Libraries, 2021) Kelley, Sarah Ariel; Blackstock, Silas C.; University of Alabama Tuscaloosa
    Nitrosoarenes (Ar-N=O) were first reported by Baeyer in 1874 after successful synthesis of nitrosobenzene via a diphenyl mercury reaction with nitrosyl bromide. C-nitroso compounds (R-N=O), like nitrosobenzene, fall between hydroxylamines (R-NH-OH) and nitro compounds (R-NO2) on the amine oxidation scale making them common intermediates for many synthetic amine oxidation reactions. Nitrosobenzenes exhibit a number of unique properties, which stem from their structure. A small energy gap between the HOMO (n*) and LUMO (?*) orbitals of the N=O function allows for several unique chemical and spectroscopic properties of nitrosoarenes. Nitrosobenzene and its derivatives have a blue-green color in monomeric form and reversibly dimerize to a colorless form in the solid state, thus yielding a dynamic covalent bonding reaction for this class of compounds. One area of our studies focuses on the very large (2-3 ppm) magnetic anisotropy of the nitroso group, which is evaluated for a series of ortho-substituted nitrosoarenes. The nitroso (-N=O) functions of these molecules are sterically forced into a primary (majority) orientation in the molecule by the ortho substituent, thereby allowing the NMR analysis of the magnetic environment around an oriented -N=O group at room temperature. Multiple substrates have been synthesized, including oriented 1,3-(bis)nitroso compounds, which have double the amount of shielding of the “syn” proton. A series of NMR techniques is employed to prove the NMR signal assignments for these compounds including: 1H, 13C, NOE, COSY, HSQC, and HMBC NMR spectroscopy. Also studied is the electron donor-acceptor (DA) bonding ability of the N=O group of N,N-dimethyl-4-nitrosobenzene (DMANB) and N,N-diethyl-4-nitrosobenzene (DEANB), in the monomeric state, as they complex and co-crystallize with electron-poor alkenes such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tetracyanoethylene (TCNE). Finally, encapsulation of N,N-dimethyl-4-nitrosobenzene (DMANB) and p-nitrosocumene (p-NC) by organic host molecules such as octa-acid (OA), cucurbit[7]uril (CB7), and cyclodextrins (?,?,?-cd) in aqueous solution is studied.
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    Organic Host Encapsulation Effects on Nitrosobenzene Monomer- Dimer Distribution and C-NO Bond Rotation in an Aqueous Solution
    (American Chemical Society, 2021) Varadharajan, Ramkumar; Kelley, Sarah Ariel; Jayasinghe-Arachchige, Vindi M.; Prabhakar, Rajeev; Ramamurthy, Vaidhyanathan; Blackstock, Silas C.; University of Miami; University of Alabama Tuscaloosa
    The intermolecular (monomer-dimer equilibrium) and intramolecular (C-NO and C-NMe2 rotations) dynamics of 4-nitrosocumene (1a) and 4-(N,N-dimethylamino)nitrosobenzene (1b), respectively, were found to be controlled by the medium (water) and the host environment (organic capsules and cavitands). The ability of water to shift the equilibrium toward the dimer appears to result from dipolar stabilization of the polar dimer structure and has a resemblance to water's known ability to favor organic cycloaddition reactions. In an aqueous medium, a range of organic hosts selectively include only the nitrosocumene monomer 1a. Encapsulation in the octa acid duplex (OA2) selects two 1a monomers rather than a dimer structure. Octa acid encapsulation also results in more restricted intramolecular C-N rotations of the guest 1b.