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51.
SynthesesandStudiesofPEG┐b┐PNIPABlockPolymersCAOWei-xiao**andZHANGTao(ColegeofChemistryandMolecularEnginering,PekingUniversit... 相似文献
52.
Radical anions of nitrobenzothiazoles: EPR study of conjugative properties of benzothiazolyl systems
Francesco Ciminale 《Tetrahedron letters》2004,45(30):5849-5852
The electrochemical reduction in DMSO of the five isomers of nitrobenzothiazole (NBTZ) gave quite persistent radical anions that could be easily characterised by EPR spectroscopy. By contrast, the chemical reduction in alkaline solution, that is by t-BuOK in DMSO or by glucose and MeOK in MeOH, presented some problems with 6- and 4-NBTZ, and in the case of 2-NBTZ did not provide any detectable paramagnetic species. The internal consistency of coupling constants of the nitrobenzothiazole radical anions is in good agreement with the conjugative properties of the various benzothiazolyl systems and allows rectifying a recent EPR characterisation of 6-NBTZ radical anion. 相似文献
53.
自动加速效应是自由基聚合宏观动力学的重要特征,对聚合过程和聚合产物有着重要的影响;有关自动加速效应的内容也是自由基聚合动力学教学的重难点之一。为帮助学生较好地理解和掌握自动加速效应相关内容,本文结合有关高分子化学教材,对自动加速效应的实验现象、与体型缩聚凝胶化过程的区别、产生原因、结果和影响因素等问题进行了总结和讨论。 相似文献
54.
W. Russell Bowman Anthony J. Fletcher Peter J. Lovell Elena Hernández López Graeme B.S. Potts 《Tetrahedron》2007,63(1):191-203
Amides have been successfully used as precursors of imidoyl radicals for radical cyclisation. The amides have been converted to imidoyl selanides via reaction with phosgene to yield imidoyl chlorides followed by reaction with potassium phenylselanide. Imidoyl selanides were reacted with tributyltin hydride (Bu3SnH) as the radical mediator with triethylborane or AIBN as initiators to yield imidoyl radicals for cyclisation reactions. Imidoyl radicals have been cyclised onto alkenes to yield 2,3-substituted-indoles and -quinolines and also onto pyrroles and indoles to give bi- and tricyclic heteroarenes. 相似文献
55.
Wojciech Dmowski Anna Ja?mu?na Z. Urbańczyk-Lipkowska 《Journal of fluorine chemistry》2007,128(12):1431-1438
Sodium dithionite effectively promotes the addition of dibromodifluoromethane to the exocyclic double bond of β-pinene. The reaction proceeded in a MeCN/H2O system to give almost quantitatively an adduct, 1-(2-bromo-2,2-difluoroethyl)-4-(2-bromoisopropyl)-cyclohexene, as the sole product. On treatment of the adduct with 2,2,6,6-tetramethylpiperidine elimination of HBr only from the (CH3)2CHBr group occurred to give a mixture of regioisomeric dienes, while treatment with 50% KOH under phase transfer catalysis conditions or with K2CO3 in DMF resulted in total dehydrobromination to give trienes possessing an exocyclic CHCF2 group. Surprisingly, the main course of the reactions of the adduct with DBU (1,8-diazabicyclo[5.4.0]undece-7-ene) and also with t-BuOK in THF was elimination of HBr only from the CH2CF2Br group to afford 1-(2,2-difluorovinyl)-4-(2-bromoisopropyl)cyclohexene as the main product. Catalytic hydrogenation of the adduct followed by treatment with DBU afforded a conjugated diene, 1-(2,2-difluorovinyl)-4-isopropylcyclohexene. Compounds bearing the CHCF2 group are new 1,1-difluorodienes which readily reacted with 4-phenyl-3H-1,2,4-triazoline-3,5-dione to give cycloadducts, derivatives of triazolo[1,2-α]cinnoline. 相似文献
56.
HeI photoelectron spectra have been recorded for the reaction of atomic fluorine with ethyl chloride at different reaction times. A structured band associated with a short-lived primary reaction product has been recorded with adiabatic and vertical ionization energies of (7.84±0.02) and (8.18±0.02) eV respectively. An average vibrational separation of (680±30) cm–1was observed in this band. Comparison between the experimental vertical and adiabatic ionization energies and ionization energies computed for CH3CHCl (X2A) and CH2CH2Cl (X2A) at different levels of theory led to the assignment of the observed first photoelectron band to the ionization of CH3CHCl (X2A). The observed vibrational structure was assigned to excitation of the C–Cl stretching mode in CH3CHCl+(X1A).Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail 相似文献
57.
Solution or Gas Phase? Oxidation and Radical Formation in Electrospray Ionization Mass Spectrometry (ESI MS) 下载免费PDF全文
The relationship between one‐electron (e?) oxidation processes and the formation of radical cations of endogenous and exogenous compounds in vivo is of considerable interest. This paper reports on the experiments that allow FTICR mass spectrometric (MS) detection of ion signals that are consistent with the formation of radical cations of caffeine (CA) and theophylline (TP) during electrospray ionization (ESI) in ESI FTICR MS and in on‐line electrochemistry (EC)/ESI FTICR MS in positive mode. Significantly, the signals of the radicals of CA?+ and TP?+can be enhanced by simple modifications of the operating conditions in ESI MS, facilitating investigations of radical formation and related reactions. 相似文献
58.
采用UωB97X-D/6-311+G**方法, 研究了气相、 甲苯和水中OH自由基(·OH)引发CH3SSCH3自由基阳离子(CH3SSC +, DMDS?+)裂解的反应机理, 并讨论了溶剂效应对反应的影响. 结果表明, ·OH和DMDS·+首先形成自由基耦合产物CH3S(OH)SCH3+(R1)和氢提取产物复合物[CH2=SSCH3+H2O]+(R2); 随后R1裂解直接发生 S—S键断裂协同质子转移, 而R2裂解依次发生构象变化、 C=S键亲碳加成和S—S键断裂协同质子转移. 去质子化的裂解产物为CH3SOH, CH2=S和HSCH2OH. 甲苯略微降低了裂解反应速控步骤的自由能垒. 水溶剂有利于R1裂解, 但不利于R2裂解, 尤其是单个水分子参与反应. 在气相、 甲苯和水中, 以·OH和DMDS·+为初始反应物, 虽然速控步骤的自由能垒为167.6~202.8 kJ/mol, 但裂解反应均是放热反应(?154.3~?31.4 kJ/mol). 相似文献
59.
Dr. Wenqing Wang Xiao-Hui Ma Min Liu Shuxuan Tang Xuguang Ding Yue Zhao Prof. Yuan-Zhi Tan Prof. Miklos Kertesz Prof. Xinping Wang 《Angewandte Chemie (International ed. in English)》2023,62(8):e202217788
We report on the largest open-shell graphenic bilayer and also the first example of triply negatively charged radical π-dimer. Upon three-electron reduction, bilayer nanographene fragment molecule (C96H24Ar6)2 (Ar=2,6-dimethylphenyl) ( 1 2) was transformed to a triply negatively charged species 1 23.−, which has been characterized by single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic properties on a superconducting quantum interference device (SQUID). 1 23.− features a 96-center-3-electron (96c/3e) pancake bond with a doublet ground state, which can be thermally excited to a quartet state. It consists of 34 π-fused rings with 96 conjugated sp2 carbon atoms. Spin frustration is observed with the frustration parameter f>31.8 at low temperatures in 1 23.−, which indicates graphene upon reduction doping may behave as a quantum spin liquid. 相似文献
60.
Wei Zheng Prof. XuPing Li Dr. Glib V. Baryshnikov Xueru Shan Dr. Farhan Siddique Dr. Cheng Qian Prof. Shengyin Zhao Prof. Hongwei Wu 《Angewandte Chemie (International ed. in English)》2023,62(32):e202305925
It is challenging to achieve stable and efficient radical emissions under ambient conditions. Herein, we present a rational design strategy to protect photoinduced carbonyl free radical emission through electrostatic interaction and spin delocalization effects. The host-guest system is constructed from tricarbonyl-substituted benzene molecules and a series of imidazolium ionic liquids as the guest and host, respectively, whereby the carbonyl anion radical emission can be in situ generated under the light irradiation and further stabilized by electrostatic interaction. More importantly, the anion species and the alkyl chain length of imidazolium ionic liquids show a noticeable effect on luminescence efficiency, with the highest radical emission efficiency is as high as 53.3 % after optimizing the imidazole ionic liquid's structure, which is about four times higher than the polymer-protected radical system. Theoretical calculations confirm the synergistic effect of strong electrostatic interactions and that the spin delocalization effect significantly stabilizes the radical emission. Moreover, such a radical emission system also could be integrated with a fluorescent dye to induce multi-color or even white light emission with reversible temperature-responsive characteristics. The radical emission system can also be used to detect different amine compounds on the basis of the emission changes and photoactivation time. 相似文献