scholarly journals Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

2018 ◽  
Vol 14 ◽  
pp. 2250-2258 ◽  
Author(s):  
Liudmila L Rodina ◽  
Xenia V Azarova ◽  
Jury J Medvedev ◽  
Dmitrij V Semenok ◽  
Valerij A Nikolaev
Keyword(s):  
Photochemical Reactions ◽  
Direct Photolysis ◽  
Wolff Rearrangement ◽  
Diazo Group

The sensitized photoexcitation of 2-diazocyclopentane-1,3-diones in the presence of THF leads to the insertion of the terminal N-atom of the diazo group into the α-С–Н bond of THF, producing the associated N-alkylhydrazones in yields of up to 63–71%. Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones gives only Wolff rearrangement products with up to 90–97% yield.

Direct photolysis of tetrafluoroethylene at 1849 Å

1969 ◽  
Vol 47 (20) ◽  
pp. 3871-3875 ◽  
Author(s):  
J. R. Dacey ◽  
J. G. F. Littler
Keyword(s):  
Double Bond ◽  
Fluorine Atom ◽  
Photochemical Reactions ◽  
Quantum Yields ◽  
Direct Photolysis

The photolysis of C2F4 at 1849 Å gives the following products, whose quantum yields are strongly dependent on substrate pressure: C2F6, C2F2, cyclo-C4F8, cyclo-C3F6, C3F6, C3F8, and polymer.The primary photochemical reactions are tentatively identified, and involve double bond fission and fluorine molecule and fluorine atom elimination.

Degradation of Nitrobenzene and Nitrophenols in Homogeneous Aqueous Solution

1992 ◽  
Vol 27 (1) ◽  
pp. 97-122 ◽  
Author(s):  
Ewa Lipczynska-Kochany
Keyword(s):  
Hydrogen Peroxide ◽  
Excited States ◽  
Electronic Structures ◽  
Fenton Reaction ◽  
Uv Light ◽  
Photochemical Reactions ◽  
Fenton Reagent ◽  
Direct Photolysis ◽  
Degradation Reactions ◽  
Aromatic Nitrocompounds

Abstract Degradation reactions of aqueous nitrobenzene (1), 2-nitrophenol (2), and 2,4-dinitrophenol (3) by means of the photolysis in the presence of the Fenton reagent (FeCL2/H2O2) (I) were investigated. The results were compared with those for 4-nitrophenol (4) as well as for direct photolysis (II), the photolysis in the presence of hydrogen peroxide (III) and the dark Fenton reaction (IV) of (1)–(3), reported elsewhere. In all the cases, decomposition of the aromatic nitrocompounds was observed. The best results were obtained when the solutions of nitrophenols 2–4, containing the Fenton reagent, were irradiated with the polychromic UV light. The rates of the compounds 1–4 degradation depend on their electronic structures in the ground and excited states. The mechanisms of the degradation of 1–4 by means of direct photolysis, the Fenton reaction, the photochemical reactions in the presence of hydrogen peroxide and the Fenton reaction are discussed. The developed method I is concluded to be more effective than II–IV, and therefore recommended for the elimination of the compounds 1–4 from waters and wastewaters.

Nanosecond Photodynamics Simulations of a Cis-Trans Isomerization Are Enabled by Machine Learning

2020 ◽  
Author(s):  
Jingbai Li ◽  
Patrick Reiser ◽  
André Eberhard ◽  
Pascal Friederich ◽  
Steven Lopez
Keyword(s):  
Machine Learning ◽  
Neural Networks ◽  
Excited State ◽  
Adaptive Sampling ◽  
Computational Cost ◽  
Ground Truth ◽  
Absolute Error ◽  
Photochemical Reactions ◽  
Computational Techniques ◽  
Full Potential

<p>Photochemical reactions are being increasingly used to construct complex molecular architectures with mild and straightforward reaction conditions. Computational techniques are increasingly important to understand the reactivities and chemoselectivities of photochemical isomerization reactions because they offer molecular bonding information along the excited-state(s) of photodynamics. These photodynamics simulations are resource-intensive and are typically limited to 1–10 picoseconds and 1,000 trajectories due to high computational cost. Most organic photochemical reactions have excited-state lifetimes exceeding 1 picosecond, which places them outside possible computational studies. Westermeyr <i>et al.</i> demonstrated that a machine learning approach could significantly lengthen photodynamics simulation times for a model system, methylenimmonium cation (CH<sub>2</sub>NH<sub>2</sub><sup>+</sup>).</p><p>We have developed a Python-based code, Python Rapid Artificial Intelligence <i>Ab Initio</i> Molecular Dynamics (PyRAI<sup>2</sup>MD), to accomplish the unprecedented 10 ns <i>cis-trans</i> photodynamics of <i>trans</i>-hexafluoro-2-butene (CF<sub>3</sub>–CH=CH–CF<sub>3</sub>) in 3.5 days. The same simulation would take approximately 58 years with ground-truth multiconfigurational dynamics. We proposed an innovative scheme combining Wigner sampling, geometrical interpolations, and short-time quantum chemical trajectories to effectively sample the initial data, facilitating the adaptive sampling to generate an informative and data-efficient training set with 6,232 data points. Our neural networks achieved chemical accuracy (mean absolute error of 0.032 eV). Our 4,814 trajectories reproduced the S<sub>1</sub> half-life (60.5 fs), the photochemical product ratio (<i>trans</i>: <i>cis</i> = 2.3: 1), and autonomously discovered a pathway towards a carbene. The neural networks have also shown the capability of generalizing the full potential energy surface with chemically incomplete data (<i>trans</i> → <i>cis</i> but not <i>cis</i> → <i>trans</i> pathways) that may offer future automated photochemical reaction discoveries.</p>

Photochemical and Electrochemical Reduction of Carbon Dioxide Catalyzed by a Polyoxometalate-Organic Photosensitizer Complex

2018 ◽  
Author(s):  
Chandan Dey ◽  
Ronny Neumann
Keyword(s):  
Carbon Dioxide ◽  
Cyclic Voltammetry ◽  
Formic Acid ◽  
Electrochemical Reduction ◽  
Mass Spectroscopy ◽  
Photochemical Reactions ◽  
Reducing Agent ◽  
Covalent Attachment ◽  
Hybrid Complex ◽  
Open Face

<p>A manganese substituted Anderson type polyoxometalate, [MnMo<sub>6</sub>O<sub>24</sub>]<sup>9-</sup>, tethered with an anthracene photosensitizer was prepared and used as catalyst for CO<sub>2</sub> reduction. The polyoxometalate-photosensitizer hybrid complex, obtained by covalent attachment of the sensitizer to only one face of the planar polyoxometalate, was characterized by NMR, IR and mass spectroscopy. Cyclic voltammetry measurements show a catalytic response for the reduction of carbon dioxide, thereby suggesting catalysis at the manganese site on the open face of the polyoxometalate. Controlled potentiometric electrolysis showed the reduction of CO<sub>2</sub> to CO with a TOF of ~15 sec<sup>-1</sup>. Further photochemical reactions showed that the polyoxometalate-anthracene hybrid complex was active for the reduction of CO<sub>2</sub> to yield formic acid and/or CO in varying amounts dependent on the reducing agent used. Control experiments showed that the attachment of the photosensitizer to [MnMo<sub>6</sub>O<sub>24</sub>]<sup>9-</sup> is necessary for photocatalysis.</p><div><br></div>

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