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Full-Text Articles in Materials Chemistry
Time-Resolved Resonance Raman And Computational Investigation Of The Influence Of 4-Acetamido And 4-N-Methylacetamido Substituents On The Chemistry Of Phenylnitrene, Jiaden Xue, Shubham Vyas, Yong Du, Hoi-Ling Luk, Yung-Ping Chuang, Tracy Yuen Sze But, Patrick H. Toy, Jin Wang, Arthur Winter, David Lee Phillips, Christopher M. Hadad, Matthew S. Platz
Time-Resolved Resonance Raman And Computational Investigation Of The Influence Of 4-Acetamido And 4-N-Methylacetamido Substituents On The Chemistry Of Phenylnitrene, Jiaden Xue, Shubham Vyas, Yong Du, Hoi-Ling Luk, Yung-Ping Chuang, Tracy Yuen Sze But, Patrick H. Toy, Jin Wang, Arthur Winter, David Lee Phillips, Christopher M. Hadad, Matthew S. Platz
Arthur Winter
A time-resolved resonance Raman (TR3) and computational investigation of the photochemistry of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide in acetonitrile is presented. Photolysis of 4-acetamidophenyl azide appears to initially produce singlet 4-acetamidophenylnitrene which undergoes fast intersystem crossing (ISC) to form triplet 4-acetamidophenylnitrene. The latter species formally produces 4,4′-bisacetamidoazobenzene. RI-CC2/TZVP and TD-B3LYP/TZVP calculations predict the formation of the singlet nitrene from the photogenerated S1 surface of the azide excited state. The triplet 4-acetamidophenylnitrene and 4,4′-bisacetamidoazobenzene species are both clearly observed on the nanosecond to microsecond time-scale in TR3 experiments. In contrast, only one species can be observed in analogous TR3 experiments after …
2-(3,5-Dinitrophenyl)-1,3-Dithiane Carbanion: A Benzylic Anion With A Low Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, William H. Coldren, Daniel E. Falvey
2-(3,5-Dinitrophenyl)-1,3-Dithiane Carbanion: A Benzylic Anion With A Low Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, William H. Coldren, Daniel E. Falvey
Arthur Winter
Calculations at the DFT level predict that benzyl anions with strong π-electron-withdrawing groups in the meta position(s) have low energy diradical or triplet electronic states. Specifically, the 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion is predicted to have nearly degenerate singlet and triplet states at the (U)B3LYP level as a free anion. Its lithium ion pair is predicted to be a ground-state triplet with a substantial (26 kcal/mol) singlet–triplet energy gap. Experiments on this anion using chemical trapping, NMR, and the Evans method strongly suggest that this anion is either a triplet or a ground-state singlet with a very low energy triplet state.
Photochemical Heterolysis Of 3,5-Bis(Dimethylamino)Benzyl Alcohols And Esters: Generation Of A Benzyl Cation With A Low-Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, Daniel E. Falvey
Photochemical Heterolysis Of 3,5-Bis(Dimethylamino)Benzyl Alcohols And Esters: Generation Of A Benzyl Cation With A Low-Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, Daniel E. Falvey
Arthur Winter
An earlier computational study (CASPT2/pVDZ) by Winter et al. predicts the 3,5-bis(dimethylamino)benzyl cation to have nearly degenerate singlet and triplet states. Through product studies it is demonstrated that photolysis of 3,5-bis(dimethylamino)benzyl alcohol and its corresponding acetate and phenylacetate esters in alcoholic solvents produces a solvent incorporated adduct, 3,5-bis(dimethylamino)benzyl ethers, and 3,5-bis(dimethylamino)toluene.
Vinyl Cations Substituted With Β Π-Donors Have Triplet Ground States, Arthur Winter, Daniel E. Falvey
Vinyl Cations Substituted With Β Π-Donors Have Triplet Ground States, Arthur Winter, Daniel E. Falvey
Arthur Winter
Computations at the CASPT2, CBS-QB3, and B3LYP levels of theory demonstrate that β-substitution of vinyl cations with π-donors switches the ground state of these ions from the familiar closed-shell singlet state to a carbene-like triplet state similar to the electronic state of triplet phenyl cations. Although the parent vinyl cation is a ground-state singlet species with a very large energy gap to the lowest energy triplet state, substituting the β hydrogens with just one strong π-donor (e.g., NH2, NMe2, OMe) or two moderate π-donors (e.g., F, OH, Ar, vinyl) makes the triplet state the computed ground electronic state. In many …
Photoaffinity Labeling Via Nitrenium Ion Chemistry: Protonation Of The Nitrene Derived From 4-Amino-3-Nitrophenyl Azide To Afford Reactive Nitrenium Ion Pairs, Valentyna Voskresenska, R. Marshall Wilson, Maxim Panov, Alexander N. Tarnovsky, Jeanette A. Krause, Shubham Vyas, Arthur Winter, Christopher M. Hadad
Photoaffinity Labeling Via Nitrenium Ion Chemistry: Protonation Of The Nitrene Derived From 4-Amino-3-Nitrophenyl Azide To Afford Reactive Nitrenium Ion Pairs, Valentyna Voskresenska, R. Marshall Wilson, Maxim Panov, Alexander N. Tarnovsky, Jeanette A. Krause, Shubham Vyas, Arthur Winter, Christopher M. Hadad
Arthur Winter
Phenyl azides with powerful electron-donating substituents are known to deviate from the usual photochemical behavior of other phenyl azides. They do not undergo ring expansion but form basic nitrenes that protonate to form nitrenium ions. The photochemistry of the widely used photoaffinity labeling system 4-amino-3-nitrophenyl azide, 5, has been studied by transient absorption spectroscopy from femtosecond to microsecond time domains and from a theoretical perspective. The nitrene generation from azide 5 occurs on the S2 surface, in violation of Kasha’s rule. The resulting nitrene is a powerful base and abstracts protons extremely rapidly from a variety of sources to form …
Carbazolyl Nitrenium Ion: Electron Configuration And Antiaromaticity Assessed By Laser Flash Photolysis, Trapping Rate Constants, Product Analysis, And Computational Studies, Arthur Winter, Harry H. Gibson, Daniel E. Falvey
Carbazolyl Nitrenium Ion: Electron Configuration And Antiaromaticity Assessed By Laser Flash Photolysis, Trapping Rate Constants, Product Analysis, And Computational Studies, Arthur Winter, Harry H. Gibson, Daniel E. Falvey
Arthur Winter
Laser flash photolysis of 1-(carbazol-9-yl)-2,4,6-trimethylpyridinium tetrafluoroborate generates the carbazolyl nitrenium ion (τ = 333 ns, kobs = 3.0 × 106 M-1s-1) having absorption bands at 570 and 620 nm in CH3CN. The nitrenium ion is found to have reactivity comparable to structurally similar closed-shell diarylnitrenium ions, but spectroscopic evidence favors an open-shell singlet diradical assignment for the observed nitrenium ion. The carbazolyl nitrenium ion is also more reactive than diarylnitrenium ions as a likely result of antiaromatic character. Ab initio and hybrid DFT calculations were performed to address the degree of antiaromaticity in this and similar nitrenium ions through analysis …
Benzylic Cations With Triplet Ground States: Computational Studies Of Aryl Carbenium Ions, Silylenium Ions, Nitrenium Ions, And Oxenium Ions Substituted With Meta Π Donors, Arthur Winter, Daniel E. Falvey, Christopher J. Cramer, Benjamin F. Gherman
Benzylic Cations With Triplet Ground States: Computational Studies Of Aryl Carbenium Ions, Silylenium Ions, Nitrenium Ions, And Oxenium Ions Substituted With Meta Π Donors, Arthur Winter, Daniel E. Falvey, Christopher J. Cramer, Benjamin F. Gherman
Arthur Winter
Density functional theory (B3LYP/6-31G(d,p)) was used to predict the effect of meta substitution on aryl cationic (Ar−X+) species, including aryloxenium ions, arylsilylenium ions, arylnitrenium ions, and arylcarbenium ions. Multireference second-order perturbation theory (CASPT2) calculations were used to benchmark the quantitative accuracy of the DFT calculations for representative systems. Substituting the meta positions on these species with π donors stabilizes a π,π* diradical state analogous to the well-known m-xylylene diradical. Notably, the 3,5-bis(N,N-dimethylamino)benzyl cation is predicted to have a triplet ground state by 1.9 kcal/mol by DFT and to have essentially degenerate singlet−triplet states at the CASPT2(10,9) level of theory. Adding …
Photochemical Generation Of Nitrenium Ions From Protonated 1,1-Diarylhydrazines, Arthur Winter, Selina I. Thomas, Andrew C. Kung, Daniel E. Falvey
Photochemical Generation Of Nitrenium Ions From Protonated 1,1-Diarylhydrazines, Arthur Winter, Selina I. Thomas, Andrew C. Kung, Daniel E. Falvey
Arthur Winter
Laser flash photolysis experiments, chemical trapping studies, and time-dependent density functional theory calculations demonstrate that photolysis of protonated 1,1-diarylhydrazines generates N,N-diarylnitrenium ions.
Effect Of Meta Electron-Donating Groups On The Electronic Structure Of Substituted Phenyl Nitrenium Ions, Arthur Winter
Effect Of Meta Electron-Donating Groups On The Electronic Structure Of Substituted Phenyl Nitrenium Ions, Arthur Winter
Arthur Winter
Density functional theory (UB3LYP/6-31G(d,p)) was used to determine substituent effects on the singlet−triplet-state energy gap for 21 meta-substituted phenylnitrenium ions. It was found that strongly electron-donating substituents stabilize the triplet state relative to the singlet state. With sufficiently strong meta electron donors (e.g., m,m‘-diaminophenylnitrenium ion) the triplet is predicted to be the ground state. Analysis of equilibrium geometries, Kohn−Sham orbital distributions, and Mulliken spin densities for the triplet states of this series of nitrenium ions leads to the conclusion that there are two spatially distinct types of low-energy triplet states. Simple arylnitrenium ions such as phenylnitrenium ions as well as …