15300-82-0Relevant academic research and scientific papers
Photochemical generation of 9h-fluorenyl radicals
Dyblenko, Tatiana,Chtchemelinine, Andrei,Reiter, Ryan,Chowdhury, Ruhul Q.,Enaya, Alexander,Afifi, Hanan,Fournier, Rene,Mladenova, Gabriela,Lever, Alfred Barry P.,Lee-Ruff, Edward
, p. 470 - 475 (2014/04/03)
A series of 9-substituted fluorenols and 9,9′-disubstituted-9, 9′-bifluorenyls were irradiated to give products derived from fluorenyl radicals. Product distribution was solvent dependent. A TEMPO adduct was isolated from the photoexcitation of 9-fluorenol. An unusual unsymmetrical 3,9′-bifluorenyl was observed from the photolysis of 9- trifluoromethylfluorenol and 9,9′-di(trifluoromethyl)-9,9′- bifluorenyl in more polar or hydrogen-bonding solvents. The electronic nature of 9-substituted fluorenyl radicals was probed using theoretical calculations showing the dipolar character of species with electron-deficient groups. These constitute the first examples of "doubly destabilized" radicals. Substituted 9-fluorenols and 9,9′-bifluorenyls undergo photolysis to give products derived from 9-fluorenyl radicals. These intermediates decay by hydrogen abstraction giving 9H-fluorenes, or coupling to 9,9′bifluorenyls. The 9-trifluoromethyl-9-fluorenyl radical undergoes an unusual coupling to the unsymmetrical 9,3′-bifluorenyl.
Direct observation of a doubly destabilized cation
Afifi, Hanan,Mikhailine, Alexandre,Mladenova, Gabriela,Chtchemelinine, Andrei,Sultana, Israt,Dyblenko, Tatiana,Danilov, Evgeny,Fournier, Rene,Lee-Ruff, Edward
experimental part, p. 343 - 354 (2012/07/03)
The 9-fluorenyl cation is a member of the 4N Hueckel antiaromatic series of intermediates, first observed by time-resolved spectroscopy on UV photo-excitation of 9-fluorenol.[1] 9-Trifluoromethyl-9-fluorenol incorporating an electron-withdrawing substituent was subjected to preparative and laser flash photolysis. Photoproduct studies in methanol indicated products derived from the corresponding fluorenyl cation and radical intermediates. Time-resolved spectroscopy in hexafluoroisopropanol (HFIP) showed a transient which was assigned to the corresponding cation as evident from methanol quenching. The lifetimes and methanol quenching rates of this transient was compared with that of 9- methylfluorenyl cation. The kinetic stabilities of these ions were compared to thermodynamic parameters obtained from theoretical calculations. ARKAT-USA, Inc.
Controlling parameters for radical cation fragmentation reactions: Origin of the intrinsic barrier
Shukla, Deepak,Liu, Guanghua,Dinnocenzo, Joseph P.,Farid, Samir
, p. 744 - 757 (2007/10/03)
C - C bond cleavages of radical cations of 2-substituted benzothiazoline derivatives were investigated to determine the parameters controlling the fragmentation rate constants. In spite of the low oxidation potentials of the compounds, fragmentation rate constants greater than 1 x 106 s -1 could be achieved through weakening of the fragmenting bond by substituents that stabilize the radical fragment and exert steric crowding. A quantitative assessment of the relative roles of radical stabilization vs. steric effects to weaken the fragmenting C - C bond was achieved through DFT calculations. The calculated activation enthalpies matched reasonably well with the experimentally determined values. A thermokinetic analysis revealed that the fragmentations of benzothiazoline radical cations have relatively large intrinsic kinetic barriers, ascribed to the delocalized nature of the product radical and cation fragments. Interestingly, the same factors that lead to the large intrinsic barriers led, simultaneously, to large thermodynamic driving forces for the fragmentations, which should lead to lower activation barriers. These effects oppose each other kinetically and provide important insight into the design of fast radical ion fragmentation reactions.
Arene Hydrides, 8. - SET vs. Nucleophilic Attack in Reactions of α-Bromoisobutyrophenone with Carbanions. Fragmentation of the Anion of Tetrahydrobianthracene
Werry, Juergen,Stamm, Helmut,Sommer, Andreas
, p. 1553 - 1562 (2007/10/02)
SET is the main reaction pathway between α-bromoisobutyrophenone (1) and the carbanions 7a-j- of diarylmethanes or disubstituted acetonitriles: 7- 7. + e and e + 1 Br- PhCOCMe2. (3).Main secon
Distinguishing between Polar and Electron-Transfer Mechanisms for Reactions of Anions with Alkyl Halides
Bordwell, F. G.,Wilson, Craig A.
, p. 5470 - 5474 (2007/10/02)
9-Substituted fluorenide carbanions in the series 9-MeFl-, 9-MeO-Fl-, and 9-Me2N-Fl-, which have nearly the same basicities but become progressively easier to oxidize, were selected as a test trio to probe for electron-transfer (eT-) components or radical-pair intermediates in reactions with alkyl halides.The trio members were shown to undergo eT- at progressively faster rates (>102 rate span) with two different types of single-electron acceptors, as expected- On the other hand, with PhCH2Cl, i-BuBr, or i-BuI, SN2 products were formed in a rate order that was the reverse of that established as characteristic of eT-.Reactions of the more sterically hindered 9-i-Pr2N-Fl- ion with PhCH2Cl or i-BuI to give SN2 products were over 1400 times slower than those with 9-MeFl-, whereas the eT- rate with c-C6H10(NO2)Ts was eight times faster.On the other hand, reactions of the test trio with F3CCH2I, which is known to react slowly in SN2 reactions, gave the reactivity order characteristic of eT-, and radical-type products were formed.For this reaction, a plot of log kobsd vs.Eox(A-) for seven 9-G-Fl- ions, wherein the bulk and radical-stabilizing ability of G was varied, was linear.This result shows that Eox(A-) is a good measure of eT- ability and that eT- rates are insensitive to steric effects in either the donor or acceptor that cause larger rate retardations in polar SN2 reactions.
Reactions of Carbanions with Electron Acceptors
Bordwell, Frederick G.,Clemens, Anthony H.,Smith, Donald E.,Begemann, John
, p. 1151 - 1156 (2007/10/02)
Second-order rate constants for reactions of families of 9-substituted fluorenide ions, 9-R-Fl(-), and related carbanions in Me2SO solution with the electron acceptors PhSO2CH2Br, PhSO2CH(Ph)Br, PhSO2C(Me)(Ph)Br, Me2CBr2, Me2C(NO2)X, PhS(O)CH2Cl, Me2C(SO2Ph)2, and Ph2I(+)Cl(-) have been measured.The carbanions used varied in basicity over a range of about 20pKHA units.For a given family, Broensted plots of log k vs. pKHA were linear, with slopes usually near unity.The relative order of rate constants correlated for the most part with the order of reduction potentials of the electron acceptors.The carbanions were converted by the electron acceptors to dimers, i.e., 9-R-Fl- -> (9-R-Fl)2, by way of a single electron transfer (e-T) mechanism.The Broensted lines for the e-T reactions of the GC6H4C(Me)CN- ion family (G = p-Cl, H, and p-Me) and the 9-t-BuFl- ion family were displaced below that of the 9-MeFl- ion family (slower rates); the kinetic points for PhC(Me)SO2Ph- and Ph2CSO2Ph- ions fell near the 9-t-BuFl- ion family line.It is demonstrated that carbanions too weakly basic to undergo thermal e-T with a given electron acceptor can be made to undergo comparable e-T reactions under photostimulation.
Broensted Correlations for Electron Transfer from Carbanions to Halomethyl Phenyl Sulfone and 1,1-Dinitroalkane-Type Acceptors
Bordwell, Frederick G.,Clemens, Anthony H.
, p. 2510 - 2516 (2007/10/02)
9-Substituted fluorenyl carbanions, 9-G-Fl(1-), with G = Ar or Me, have been dimerized to (9-G-Fl)2 by reaction in Me2SO solution with PhSO2CH2X and R2C(NO2)X electron acceptors.Rate measurements revealed the following electron-accepting abilities: c-C6H10(NO2)2 > Me2C(NO2)2 > PhSO2CH2Br, PhSO2CH2I > c-C6H10(NO2)CN > c-C6H10(NO2)SO2C7H7 > Me2C(NO2)SO2C7H7 > PhSO2CH2Cl.The rate-limiting step in these reactions is electron transfer from 9-G-Fl(1-) to the electron acceptor.Plots of log k vs. pKa of 9-G-FlH are linear with a slope near unity for all seven electron acceptors studied.We conclude that a Broensted β of unity is characteristic of electron transfer from carbanions to electron acceptors in Me2SO solution.This is interpreted to mean that the changes in ΔG0 brought about by changes in the basicity of the carbanion are matched by changes in ΔG(excit.), which correspond to the difference in the energy gap between the HOMO of the donor and the LUMO of the acceptor.
REACTIVITY OF ORGANOTIN COMPOUNDS. XXII. REACTIONS OF ORGANOTIN COMPOUNDS WITH o-NITROBENZENESULFENYL CHLORIDE
Kashin, A. N.,Bumagin, N. A.,Beletskaya, I. P.,Reutov, O. A.
, p. 2190 - 2195 (2007/10/02)
The reaction of organotin compounds RSnMe3 and of cyclohexenyloxytriethyltin (VII) with o-nitrobenzenesulfenyl chloride (VIII) in methylene chloride under vacuum conditions was investigated.In the reactions of the organotin compounds (IV - VII) with o-nitrobenzenesulfenyl chloride (VIII) the corresponding sulfides are formed with quantitative yields.In the reactions ofcompounds (I) and (II) with (VIII) sulfides, fluorenyl dimers, and (o-NO2C6H4S)2 are obtained, and the yield of the sulfides decreases in the presence of atmospheric oxygen.In the reaction of compound (III) with (VIII) only the oxidation products (9-C6H5C13H8)2 and (o-NO2C6H4S)2 are formed.Possible reaction mechanisms are discussed.
