Acidities and homolytic bond dissociation energies (BDEs) of benzyl-type carbon-hydrogen bonds in sterically congested substrates

Bordwell, F. G.; Cheng, Jianbo; Satish, A. V.; Twyman, Cary

doi:10.1021/jo00050a032

Cited by 37 publications

(21 citation statements)

References 2 publications

(4 reference statements)

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“…Then, the propagation proceeds by the addition of the free radical. For the oligoimides in their excited state, unpaired electrons can be stabilized by resonance stabilization of adjacent phenyl rings [ 57 , 58 ]. The resonance stabilization demands overlap of the p orbitals of the one-electron-occupied ethynyl carbons and that of phenyl-carbons that connect to them, which may result in allene-like structure between C 1 and C 2 ( Scheme 3 ).…”

Section: Resultsmentioning

confidence: 99%

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure–Melt Stability Relationship

Hong

Yuan

et al. 2021

Polymers

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Phenylethynyl-terminated aromatic polyimides meet requirements of resin transfer molding (RTM) and exhibits high glass transition temperature (Tg) were prepared. Moreover, the relationship between the polyimide backbones structure and their melting stability was investigated. The phenylethynyl-terminated polyimides were based on 4,4’-(hexafluorosiopropylidene)-diphthalic anhydride (6FDA) and different diamines of 3,4’-oxydianiline (3,4’-ODA), m-phenylenediamine (m-PDA) and 2,2’-bis(trifluoromethyl)benzidine (TFDB) were prepared. These oligoimides exhibit excellent melting flowability with wide processing temperature window and low minimum melt viscosities (< 1 Pa·s). Two of the oligoimides display good melting stability at 280–290 °C, which meet the requirements of resin transfer molding (RTM) process. After thermally cured, all resins show high glass transition temperatures (Tgs, 363–391 °C) and good tensile strength (51–66 MPa). The cure kinetics studied by the differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (13C NMR) characterization and density functional theory (DFT) definitely confirmed that the electron-withdrawing ability of oligoimide backbone can tremendously affect the curing reactivity of terminated phenylethynyl groups. The replacement of 3,4’-ODA units by m-PDA or TFDB units increase the electron-withdrawing ability of the backbone, which increase the curing rate of terminated phenylethynyl groups at processing temperatures, hence results in the worse melting stability.

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Section: Resultsmentioning

confidence: 99%

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure–Melt Stability Relationship

Hong

Yuan

et al. 2021

Polymers

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“…The starting material for our research was Nn-4H, a molecule with two non-aromatic rings bearing each two methylene groups susceptible of being dehydrogenated 54 . After deposition, the molecules preferentially physisorbed at the corners of the herringbone surface (red contours in Figure 1a Figure S4) and is much lower than the C-H bond dissociation energy 39,55 , which indicates that the energy dissipated from vibronic excitations cleaves the bonds. We note here that the C sp3 -H bonds in the methylene groups are the anticipated breaking points, since their bond-dissociation energy (3.4 eV for 9,10-dihydroanthracene 39,55 ) is lower compared to C sp2 -H bonds in the aromatic rings (e.g.…”

Section: Resultsmentioning

confidence: 99%

Nonacene Generated by On-Surface Dehydrogenation

et al. 2017

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The on-surface synthesis of nonacene has been accomplished by dehydrogenation of an air-stable partially saturated precursor, which could be aromatized by using a combined scanning tunneling and atomic force microscope as well as by on-surface annealing. This transformation allowed the in-detail analysis of the electronic properties of nonacene molecules physisorbed on Au(111) by scanning tunneling spectroscopy measurements. The spatial mapping of molecular orbitals was corroborated by density functional theory calculations. Furthermore, the thermally induced dehydrogenation uncovered the isomerization of intermediate dihydrononacene species, which allowed for their in-depth structural and electronic characterization.

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“…With strong evidence for a proton abstraction from a benzyl carbon, the question arose as what base on the enzyme would be strong enough since the pKa of a benzyl proton is expected to be ∼25 [26]? Structural analysis of the active sites in either MAO A or in MAO B show there are no basic amino acid residues that could possibly function as a proton acceptor [13,14].…”

Section: Proposed Mechanism Of C-h Bond Cleavage In Mao Catalysismentioning

confidence: 99%

Structural insights into the mechanism of amine oxidation by monoamine oxidases A and B

Edmondson¹,

Binda²,

Mattevi³

2007

Archives of Biochemistry and Biophysics

184

144

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Due to their pharmacological importance in the oxidation of amine neurotransmitters, the membrane-bound flavoenzymes monoamine oxidase A and monoamine oxidase B have attracted numerous investigations and, as a result, two different mechanisms; the single electron transfer and the polar nucleophilic mechanisms, have been proposed to describe their catalytic mechanisms. This review compiles the recently available structural data on both enzymes with available mechanistic data as well as current NMR data on flavin systems to provide an integration of the approaches. These conclusions support the proposal that a polar nucleophilic mechanism for amine oxidation is the most consistent mechanistic scheme as compared with the single electron transfer mechanism.

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Acidities and homolytic bond dissociation energies (BDEs) of benzyl-type carbon-hydrogen bonds in sterically congested substrates

Cited by 37 publications

References 2 publications

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure–Melt Stability Relationship

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure–Melt Stability Relationship

Nonacene Generated by On-Surface Dehydrogenation

Structural insights into the mechanism of amine oxidation by monoamine oxidases A and B

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