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1.
Shinro Yasui Md. Mizanur Rahman Badal Shinjiro Kobayashi Masaaki Mishima 《Journal of Physical Organic Chemistry》2014,27(12):967-972
Laser flash photolysis‐time‐resolved infrared spectroscopy (LFP‐TRIR) was performed on an acetonitrile or dichloromethane solution of triarylphosphines, Ar3P, in air. A transient spectrum consisting of several absorption bands appeared in the region of 1050–1300 cm−1 on the TRIR on a microsecond timescale, which disappeared on a millisecond timescale. To identify the observed transient intermediate, the IR spectra of possible intermediates of the photoreaction were simulated by theoretical calculations based on density functional theory (DFT). The IR spectrum simulated for the phosphine peroxidic radical cation, Ar3P+OO•, well predicted the observed IR spectrum, showing that Ar3P+OO• is formed as a transient intermediate upon the LFP of Ar3P in air. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
Ryoichi Akaba Masaki Kamata Akiko Koike Ken-Ichi Mogi Yasunao Kuriyama Hirochika Sakuragi 《Journal of Physical Organic Chemistry》1997,10(11):861-869
Photoinduced electron transfer reactions of trans-stilbene sensitized by 2,4,6-triphenylthiapyrylium tetrafluoroborate (STPP) were carried out by steady-state and laser flash photolysis techniques in the presence and absence of oxygen in dichloromethane. Rapid dimerization of the trans-stilbene cation radical with its neutral species was observed, as previously observed in 2,4,6-triphenylpyrylium tetrafluoroborate (TPP)-sensitized reactions in dichloromethane. Electrochemical and photophysical properties such as fluorescence quantum yield and T–T absorption spectrum of STPP were also studied, and the results were compared with those for TPP. The properties of STPP as an electron transfer sensitizer are discussed. © 1997 John Wiley & Sons, Ltd. 相似文献
3.
Nicolas P.‐A. Monney Thomas Bally Bernd Giese 《Journal of Physical Organic Chemistry》2015,28(5):347-353
Long distance electron transfer in proteins requires relay stations that can be transitorily oxidized or reduced. Although individual prolines cannot assume this function, because of their high ionization energy, it has been shown that polyprolines have the ability to transfer charges. In order to determine the role of the proline in the hole distribution and transport within a PheProPhe tripeptide, the radical cation of a model compound where the phenylalanines carry two or three methoxy groups, respectively, was generated by flash photolysis. Surprisingly, after equilibration, about two thirds of the holes were found to reside on the phen(OMe)2 instead of the more easily oxidizable phen(OMe)3 moiety. DFT calculations showed that, in most of the accessible conformations, the phen(OMe)2• +‐moiety profits more from stabilization by N‐ and/or O‐lone pairs of neighboring amide groups than the phen(OMe)3• + moiety can, which explains the apparently counterthermodynamic hole distribution. Similar calculations showed that, in several conformers of the natural PheProPhe radical cation, the unpaired electron is delocalized over two amide groups, by residing in a σ MO which links the N‐lone pair of the central proline unit with the O‐lone pair of a proximate amino acid, through hyperconjugation via the intervening C―Cα σ‐bond. The same pattern is found in a model compound, N‐acetylproline dimethylamide. It seems that prolines favor conformers which foster hyperconjugation of two amide groups, which lowers the ionization energy of peptides. One should thus consider such interacting amide groups as potential relay stations in the course of electron transfer in polyprolines. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
The chloroform-d solution of diphosphine, 1,n-bis(diphenylphosphino)alkane (Ph2P(CH2)nPPh2; n = 1-6), was photolyzed with light from a xenon lamp in air. The progress of the reaction was followed by 31P NMR spectroscopy. The observed spectral change showed that the diphosphine is initially oxidized to diphosphine monoxide, Ph2P(═O)(CH2)nPPh2, which is further oxidized to diphosphine dioxide, Ph2P(═O)(CH2)nP(═O)Ph2. The oxidation of the diphosphine to the diphosphine monoxide took place according to first-order kinetics with respect to the concentration of the diphosphine, the first-order rate constant, kobs, being larger with increasing number of the methylene units in the spacer. The observation in kinetics is interpreted based on the conformation of the diphosphine radical cation intermediate initially generated by electron transfer from the photoexcited diphosphine to oxygen. Density functional theory (DFT) calculations predict that the diphosphine radical cation takes “folded” conformation where two phosphorus atoms are arranged closely to each other. The “folded” conformer of the diphosphine radical cation results from electrostatic interaction of these two phosphorus atoms. This conformer explains the observed dependency of kobs on the length of the spacer in the diphosphine. 相似文献
5.
Shinro Yasui Shinjiro Kobayashi Masaaki Mishima 《Journal of Physical Organic Chemistry》2016,29(9):443-451
Laser flash photolysis at 266 nm was carried out on the acetonitrile solution of triarylphosphines, Ar3P, using a Nd YAG laser under oxygen, air, and argon atmospheres by varying the Ar3P concentration. The spectral change was monitored by time‐resolved UV–Vis spectroscopy. A transient absorption that appeared on the TRUV spectrum within 100 ns after the laser flash was judged to result from the triarylphosphine radical cation, Ar3P•+, based on a comparison with previously reported spectra. The absorption decayed on a time scale of microseconds according to the first‐order kinetics, in which the first‐order rate constant, kobs, is expressed by kobs = kO2[O2] + kAr[Ar3P] + ks. The first term in this expression represents the radical coupling of Ar3P•+ with O2, whereas the second term likely results from an ionic reaction of Ar3P•+ with the parent phosphine. This finding suggests that Ar3P•+ undergoes either a radical coupling with oxygen or an ionic reaction with Ar3P to decay. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
6.
Ting‐Wei Mu Lei Liu Xiao‐Song Li Qing‐Xiang Guo 《Journal of Physical Organic Chemistry》2001,14(8):559-565
PM3 and B3LYP/3‐21G(d) calculations were performed on the inclusion complexation of cyclodextrins (CD) with radical ions. The calculations reproduced the experimental observations that the complexation of α‐CD with 1,4‐dicyanobenzene was weaker than with its radical anion, and that the complexation of β‐CD with phenothiazine was weaker than with its radical cation. On the other hand, calculations showed that the complexation of α‐CD with p‐nitrophenolate was stronger than with its radical anion and the complexation of β‐CD with viologen was stronger than with its radical cation. The different magnitudes of the interactions between the charged species and CD or water were proposed to cause such behaviors. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
7.
Calvin J. Emanuel John H. Horner Martin Newcomb 《Journal of Physical Organic Chemistry》2000,13(11):688-692
Kinetics of ring openings of 2‐phenyl‐substituted cyclobutylcarbinyl radicals were studied by laser flash photolysis methods employing N‐hydroxypyridine‐2‐thione (PTOC) esters as radical precursors. The radicals studied were (trans‐2‐phenylcyclobutyl)methyl ( 1a ), 1‐(trans‐2‐phenylcyclobutyl)ethyl ( 1b ), 1‐methyl‐1‐(trans‐2‐phenylcyclobutyl)ethyl ( 1c ), (cis‐2‐phenylcyclobutyl)methyl ( 2a ), 1‐(cis‐2‐phenylcyclobutyl)ethyl ( 2b ) and (ethoxycarbonyl),(trans‐2‐phenylcyclobutyl)methyl ( 13 ). Arrhenius parameters for radicals 1 were determined in THF and acetonitrile and those for radicals 2 were determined in THF. Rate constants for ring openings at 20 °C in units of 107 s−1 are 1.3 ( 1a ), 1.0 ( 1b ), 0.8 ( 1c ), 3.2 ( 2a ) and 3.9 ( 2b ). These ring openings are more than three orders of magnitude faster than those for the parent cyclobutylcarbinyl radicals lacking the phenyl groups. The family can be used in direct studies of radical substituent effects and as internal reporter groups for other radical reactions. A demonstration of the former application is the measurement of the kinetics of ring openings of radical 13 which rearranges with rate constants nearly equal to those of the analogous methyl‐substituted radical 1b and, unlike radicals 1 displays a polar solvent effect in the kinetics of the fragmentation reaction. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
8.
María Virginia Mirífico José Alberto Caram Ana María Gennaro Carlos Jorge Cobos Enrique Julio Vasini 《Journal of Physical Organic Chemistry》2009,22(10):964-970
Radical anions of 3,4‐aryl disubstituted 1,2,5‐thiadiazole 1,1‐dioxide were obtained by chemical and electrochemical reduction of their substrates, and characterized by ESR spectroscopy and cyclic voltammetry. The radical anion of the phenanthro[9,10‐c]‐1,2,5‐thiadiazole 1,1‐dioxide was found to be very stable in an aprotic solvent solution and did not react readily when water was added to the aprotic solvent, or the solution was saturated with oxygen gas. The radical formation chemical reaction competed with nucleophilic addition to the C?N bond of the thiadiazoles. A possible reaction mechanism, and a common reaction intermediate, supported by density functional theory calculations, is presented for the most stable radical. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
9.
苯甲酸及其甲基取代物的激光光解研究 总被引：1，自引：1，他引：0
研究了苯甲酸及其甲基取代物在248 nm激光作用下的光电离及光激发行为,测定了光电离量子产额和激发三线态寿命及其自猝灭速率常数。实验结果显示甲基在苯环不同位置的取代对苯甲酸化合物激发三线态的影响不明显。利用分步双激光技术对苯甲酸激发态进行共振激发,对可能生成的瞬态产物进行了初步探讨。 相似文献
10.
Atnaf Admasu Matthew S. Platz Andrzej Marjcinek Jacek Michalak Anna Dra Gudmundsdttir Jerzy Gebicki 《Journal of Physical Organic Chemistry》1997,10(4):207-220
Laser flash photolysis (LFP, XeCl, 308 nm, 20 ns) of phenyldiazomethane (PDM), o-tolydiazomethane (TDM) and mesitydiazomethane (MDM) produces phenylcarbene (PC), o-tolycarbene (TC) and mesitylcarbene (MSC), respectively. Transient spectra of PC and TC could not be detected in pentane at ambient temperature; however, these carbenes could be trapped with pyridine to form UV–Vis-active ylides. The rate of formation of these ylides was resolved in CF2ClCFCl2 (Freon-113) and yields, after analysis, values of kpyr and τ, where kpyr is the absolute rate constant of the reaction of the spin equilibrated carbene with pyridine and τ is the carbene lifetime in Freon-113 in the absence of pyridine. LFP of MDM produces the transient spectra of both triplet MSC and 3,5-dimethyl-1,2-benzoquinodimethane (3,5-BQM). The lifetime of 3MSC in pentane is ca 500 ns. 3MSC reacts with pyridine with an apparent rate constant of kpyr=1·35×107 M −1 s−1. The decay of 3MSC in a variety of solvents does not lead to increased absorption of 3,5-BQM in solution, nor does the presence of a carbene scavenger (methanol) lead to a reduction in yield of 3,5-dimethyl-1,2-benzoquinodimethane upon LFP of precursor. Thus, the decay of 3MSC in solution does not lead to the formation of quinodimethane. This species (3,5-BQM) is formed, instead, by a hydrogen atom transfer in the excited state of the precursor. Product analysis reveals that the excited state rearrangement which forms xylylene is a minor process. Photolysis of MDM in a nitrogen matrix at 10 K leads to the UV–Vis spectra of matrix-isolated triplet mesitylcarbene and 3,5-BQM. The carbene rearranges slowly to 3,5-BQM in the cryogenic matrix, in contrast to its behavior in solution. © 1997 John Wiley & Sons, Ltd. 相似文献
11.
Geniece Hallett‐Tapley Frances L. Cozens Norman P. Schepp 《Journal of Physical Organic Chemistry》2009,22(4):343-348
A series of α‐vinyl arylmethyl cations were generated and studied using nanosecond laser flash photolysis. Rate constants for the decay of the substituted α‐vinyl arylmethyl cations were determined under solvolytic conditions in pure solvents and solvent mixtures of 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) and 2,2,2‐trifluoroethanol (TFE). In addition the absolute reactivity of the carbocations with added nucleophiles were obtained. The reactivities of the α‐vinyl arylmethyl cations were then compared to the reactivities of the corresponding α‐methyl, α‐phenyl, and α‐cyclopropyl arylmethyl cations. Hammett σ+ plots of each of the series of carbocations were obtained and the substituent effects on carbocation reactivity analyzed. These data show that the influence of substituent on the reactivity of the α‐vinyl carbocations was different from the substituents effects on the reactivity of the α‐methyl, α‐phenyl, and α‐cyclopropyl series. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
Formations of triplet state, molecular cation radical, and phenoxyl radical of 3,4‐methylenedioxy phenol (sesamol, SOH) in organic solvents have been investigated by laser photolysis as well as pulse radiolysis techniques. Photolysis of SOH in cyclohexane has been found to produce both triplet state (λmax ～ 480 nm) and phenoxyl radical (425–430 nm) of SOH by mono‐photonic processes. However, radical cation (λmax = 450 nm) and phenoxyl radical of SOH have been observed on radiolysis in cyclohexane. Further, radiolysis of SOH in benzene has been found to produce phenoxyl radical only. Mechanism of phenoxyl radical formation by photo‐excitation of SOH has been studied and triplet energy level of SOH is estimated to lie between 1.85 and 2.64 eV. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
13.
Photoinduced electron transfer (PET) was studied in toluene solutions of the Pd-porphyrin-quinone (Pd-PQ) dyad by flash photolysis
in the picosecond time range and by a luminescence method. It is found that Pd-PQ has a high rate of intercombination conversion
Kisc=(7.7±0.2)·1010 sec−1. Competing intramolecular PET occurs from the lower excited singlet state of the dyad with the rate constant K
et
s
=(2.7 ±0.3)·1010 sec−1. Therefore, ∼74% of excited molecules from the dyad make a transition to the triplet T1 state and 26% take part in intramolecular PET resulting in formation of radical products. The radical products relax to the
ground state with the rate constant K=(7.4±0.2)·109 sec−1.
Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina St., Minsk, 220072,
Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 11–18, January–February, 1999. 相似文献
14.
15.
Phototransformation mechanism of monuron induced by the triplet benzophenone in aqueous solution was investigated by laser flash photolysis technique, while quenching of the triplet benzophenone by monuron was studied by nanosecond transient absorption spectroscopy. The transient species in the transient absorption spectra have been identified by quantum chemistry calculations. The results show that under 355‐nm irradiation proton transfer between the triplet benzophenone and monuron happens, and monuron radical is formed and followed by dechlorination degradation reactions. This work indicated that in aqueous solution some dissolved natural organic matters are helpful to degradation of the organic pollutants under the sunlight. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
16.
The 266nm photolysis products of 4,4′-bipyridine in cyclohexane, acetonitrile, methanol, hexafluoro-propanol and H2O/HCl solutions have been investigated by time-resolved Raman spectroscopy in the nanosecond time scale. The identification of some photochemical transients and the characterization of their structure and electronic configuration are discussed. 相似文献
17.
18.
Liang Junxi Li Yu Zhang Qiang Geng Zhiyuan 《Journal of Physical Organic Chemistry》2014,27(5):392-400
The effect of halogen‐substituent on hydrogen abstraction mechanisms was studied by applying density functional theory functional calculations to the gas‐phase reactions between CHCl•− and CH4 − nXn (X = H, F, Cl; n = 0–3), and it is found that a heavier X substituent in the substrate results in a greater stabilization of corresponding complex, a lower activation energy, a faster H‐abstraction reaction, and greater exothermicity. However, CH4– reaction is more reactive than CH3F– reaction under the same condition because of dominant π‐donation from the electronegative F atom. We also explored the reactivity difference for the seven reactions in terms of factors derived from bond order, second‐order perturbative energy, and activation strain model analysis. The rate constants are evaluated over a wide temperature range of 298–1000 K by the conventional transition state theory. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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20.
《Journal of Electrostatics》2014,72(5):412-416
Many studies have been reported for contact electrification based on the electron transfer from donors to acceptors. However, the chemical structures of donors and acceptors have not been identified. Here we calculated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of model structures of mechano anions, mechano cations and mechano radicals which were produced by the heterogeneous and homogeneous scissions of covalent bonds comprising polymer main chain in vacuum at 77 K. We identified the donors are mechano anions(HOMO) and mechano radicals(HOMO), and the acceptors are mechano cations(LUMO) and mechano radicals(LUMO). The contact electrification is due to the electron transfer from the donors to the acceptors during contacting on the friction surface, and produces mosaic nano-scopic domains with opposite sign. The sign of the net charge of polymer was deduced from the number of paths of electron acceptance reaction. The relative sign of charge and position on the triboelectric series were deduced from their chemical structure. 相似文献