- Thermodynamics and kinetics of homolytic cleavage of carbon-oxygen bonds in radical anions obtained by electrochemical reduction of alkyl aryl ethers
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The properties and the reactivity of the radical anions of 4-cyanophenyl alkyl ethers and naphthyl alkyl ethers have been determined by electrochemical methods. Under electrochemical conditions homolytic dissociation is the only observed process. Cyclic voltammetry studies lead to the conclusion that this process is a stepwise one, the initially produced radical anion cleaving by a slow first order reaction followed by a second electron transfer in a DISP1 mechanism. A Marcus type relationship between the cleavage rate constants and the standard free energy of the reaction leads to an intrinsic barrier in the range of 0.7 to 0.8 eV. The analysis of the intrinsic barrier values indicates that solvent organisation represents a modest contribution, the bond dissociation energy of the radical anion (structural contribution I being the main factor in the total barrier. Previously unknown bond dissociation energies of naphthyl ethers have been estimated using the correlations established in this work.
- Andrieux, Claude P.,Farriol, Maria,Gallardo, Iluminada,Marquet, Jordi
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Read Online
- Widely Applicable Hydrofluorination of Alkenes via Bifunctional Activation of Hydrogen Fluoride
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Expanding the use of fluorine in pharmaceuticals, agrochemicals and materials requires a widely applicable and more efficient protocol for the preparation of fluorinated compounds. We have developed a new generation nucleophilic fluorination reagent, KHSO4-13HF, HF 68 wt/wt %, that is not only easily handled and inexpensive but also capable of hydrofluorinating diverse, highly functionalized alkenes, including natural products. The high efficiency observed in this reaction hinges on the activation of HF using a highly "acidic" hydrogen bond acceptor.
- Lu, Zhichao,Zeng, Xiaojun,Hammond, Gerald B.,Xu, Bo
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supporting information
p. 18202 - 18205
(2017/12/28)
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- A highly efficient approach to [4]pseudocatenanes by threefold metathesis reactions of a triptycene-based tris[2]pseudorotaxane
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A triptycene-based homotritopic host was designed and synthesized. Assembly of the host with a bisbenzylammonium salt containing terminal double bonds resulted in a tris[2]pseudorotaxane, which further performed the threefold metathesis reaction and then
- Zhu, Xiao-Zhang,Chen, Chuan-Feng
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p. 13158 - 13159
(2007/10/03)
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- 3,8-Diazabicyclo[3.2.1]octanes and their use in the treatment of cardiac arrhythmias
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There is provided compounds of formula (I), wherein R1, R2 and Ra to Rb have meanings given in the description, which are useful in the prophylaxis and in the treatment of arrhythmias, in particular atrial and v
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- New bispidine compounds and their use in the treatment of cardiac arrhythmias
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There is provided compounds of formula (I), wherein R1, R2, R3a, R3b and R41 to R46 have meanings given in the description, which are useful in the prophylaxis and in the treatment of arrhy
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Page/Page column 20-21
(2010/01/31)
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- Substituent effects on the rate constants for the photo-claisen rearrangement of allyl aryl ethers
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The photochemistry of 11 substituted allyl 4-X- and 3-X-aryl ethers 3 (ArOCH2-CH=CH2) has been examined in both methanol and cyclohexane as solvents. The ethers react by the photo-Claisen rearrangement to give allyl substituted phenols as the major primary photoproducts, as expected from the well-established radical pair mechanism. The excited singlet state properties (absorption spectra, fluorescence spectra, fluorescence quantum yields, and singlet lifetimes) were compared with a parallel set of unreactive 4-X- and 3-X-anisoles 4. The excited-state properties of three substituted 4-X-aryl 4-(1-butenyl) ethers 14 (ArOCH2CH2-CH=CH2) were also examined. The model compounds 4 and the reactive allyl ethers 3 have essentially identical rate constants for the excited-state processes with the exception of khoms, the rate constant for homolytic cleavage from S1 of the allyl ethers to give the radical pair. The difference between the fluorescence quantum yields and/or singlet lifetimes for 3 and 4 were used to obtain values of khoms for all of the allyl ethers. These values exhibit a large substituent effect, spanning almost 2 orders of magnitude with electron-donating groups (CH3O, CH3) accelerating the reaction and electron-withdrawing ones (CN, CF3) slowing it down. The parallel range of rate constants observed in both methanol and cyclohexane indicates that ion pairs are not important intermediates in these rearrangements. Quantum yields of reaction (Φr) for several of the more reactive ethers demonstrate that neither these values nor rate constants of reaction (khomr) derived from them are reliable measures of the actual excited-state process. In fact, the khomr values are significantly lower than the khoms ones, indicating that the radical pairs undergo recombination to generate starting material. Finally, the khoms rate constants were found to parallel a trend for the change in bond dissociation energy (ΔBDE) for the O-C (allyl) bond of the allyl ethers, indicating that other possible substituent effects are of minor importance.
- Pincock, Alexandra L.,Pincock, James A.,Stefanova, Roumiana
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p. 9768 - 9778
(2007/10/03)
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- Intramolecular Photocycloaddition of 4-Phenoxybut-1-enes: a Convenient Access to the 4-Oxatricyclo3.7>undeca-2,10-diene Skeleton
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The photochemistry of 4-phenoxybut-1-ene is markedly influenced by the presence and position of electron-withdrawing substituents on the benzene ring.A cyano substituent in the 2'-or 4'-position promotes an efficient intramolecular cycloaddition to give g
- Al-Qaradawi, Siham Y.,Cosstick, Kevin B.,Gilbert, Andrew
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p. 1145 - 1148
(2007/10/02)
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