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991.
John P. Maier 《Angewandte Chemie (International ed. in English)》1981,20(8):638-646
The radiative decay of over a hundred open-shell organic radical cations has now been established. As a result, the spectral structure of such cations in their ground and excited electronic states can be probed with resolutions of the order of ? 1 cm?1. This is achieved by means of emission and laser-induced fluorescence techniques. The analysis of the emission and excitation spectra provides the vibrational frequencies of many of the totally symmetric fundamentals of the cations in the two electronic states. In order to study the relaxation behavior of these cations under “isolated conditions”, the lifetimes and fluorescence quantum fields can be obtained by means of photoelectron-photon coincidence measurements. These data yield the radiative and non-radiative rate constants as a function of the internal energy of the cations. The structural and decay information obtained from each of these techniques is illustrated using the 1,3-pentadiyne radical cation as example. 相似文献
992.
Qiong Zhao 《Tetrahedron》2007,63(27):6296-6305
The Feldman radical oxygenation of vinylcyclopropanes is successfully applied to the synthesis of the highly substituted core of the 1,2-dioxolane natural product, plakortide E. The ratio of the desired cis-1,2-dioxolane can be enhanced by choice of cyclopropane substituents. 相似文献
993.
Xavier Vila 《Tetrahedron letters》2004,45(24):4661-4664
Intramolecular reactions between 1-(carbamoyl)dichloromethyl radicals and enones acting as radical acceptors are reported for the first time. The Bu3SnH promoted 6-exo reaction of trichloroacetamides with enones, avoiding the 1,5-hydrogen transfer, constitutes a new synthetic entry to cis-perhydoisoquinoline-3,6-diones. 相似文献
994.
本文引用50多篇文章,按引发方式不同从顺序引发剂,imiferter法,高分子引发剂法和自由基性聚合等几方面综述了自由基嵌段共聚合近10年来的新进展。 相似文献
995.
996.
Nobuhito Kurono Eiichi Honda Fumikazu Komatsu Kazuhiko Orito Masao Tokuda 《Tetrahedron》2004,60(8):1791-1801
Electrochemical reduction of haloarenes carrying 2-(1-hydroxybut-3-enyl), 2-allyloxy or N-allyl-N-methylamino group in the presence of phenanthrene as a mediator generated the corresponding aryl radicals and gave the corresponding 5-exo cyclization products in good yields. Higher regio- and stereoselectivities than those of usual radical cyclization using AIBN-Bu3SnH were achieved. 相似文献
997.
Gelsemine Support Studies: Observation of an Unusual Free Radical Cyclization-Fragmentation Sequence
Treatment of vinylogous urethanes 9a and 9b with tri-n-butyl in hydride generated a tree radical that underwent cyclization-fragmentation to afford oxindole-ketones 10 and 11 in high yield. Vinylogous urethane 13 , gave only cyclization-reduction products 15 and 16 upon treatment with tri-n-butyltin hydride at 80 °C, but also afforded a low yield of cyclization-fragmentation product 14 upon treatment with tris(trimethyl-silyl)silane at 140 °C. 相似文献
998.
Dihydroxybenzoic acid (DHB) analogues substituted at the 5-position can act as UV matrices at a wavelength of 337 nm, even when their absorption maxima are shifted past this particular wavelength.Modification of a matrix with a chiral ligand γ-(3-carboxy-4-hydroxy-anilide) (GCA) allowed it to differentiate between chiral isomers of tryptophan and also gave different intensities for glucose isomers, including structural dimers of glucose (cellobiose and maltose).An analogue that had one free hydroxyl group at the 2-OH position and a modification at the 5-position (MY10) gave protonated substance P (SP, analyte) peaks, similar in intensity to the not derivatised parent 2,5-dihydroxybenzoic acid indicating that the 5-OH position is not an important structural component.Another analogue that resembled a ‘dendrimeric’ structure of DHB (M552), also acted as a matrix, although its absorption maxima was at 552 nm suggesting the possibility of it being used at other wavelengths in addition to 337 nm.The DHB radical was complexed to a nitrone ‘spin-trap’. On complexion, the peptide (SP) peak intensity decreased. Addition of either radical initiators, such as 2,2-azobis(iso-butyronitrile) AIBN and tert-butylperoxide, or other radicals such as 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) gave rise to higher analyte peak intensities for [SP+Na]+.It is thought that the DHB neutral radical is an intermediary in the protonation of the analyte. The photo-fragments of DHB, specifically the m/z 137 species, may also take part in proton transfer since possible mass analogues (hydroquinone, (deoxy)benzoin) can lead to analyte enhancement. Stabilization of or an increase in the matrix radical can also lead to analyte signal enhancement. 相似文献
999.
Surface modified TiO2 nanoparticles dissolved in toluene were encapsulated in PMMA by in situ radical polymerization of methyl methacrylate initiated by 2,2′-azobisisobutyronitrile. The surface modification of the TiO2 nanoparticles (average diameter of 4.5 nm) was achieved by the formation of a charge transfer complex between TiO2 nanoparticles and 6-palmitate ascorbic acid. The surface modified TiO2/nanoparticles were characterized using UV−Vis and FTIR spectroscopy, while the obtained polymer nanocomposites were characterized using reflection and 1H NMR spectroscopy, as well as gel permeation chromatography. The influence of the TiO2 nanoparticles on the thermal properties of the PMMA matrix was investigated using thermo-gravimetric analysis and differential scanning calorimetry. The glass transition temperature of the polymer was not influenced by the presence of the nanoparticles while the thermal stability was significantly improved. 相似文献
1000.
Hongwei Wang 《European Polymer Journal》2004,40(10):2287-2290
The homogeneous polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) as betaine monomer with potassium peroxydisulfate (KPS) was kinetically investigated in water by means of FT-near IR spectroscopy. The overall activation energy of the polymerization was estimated to be 12.8 kcal/mol. The initial polymerization rate (Rp) at 40 °C was given by Rp = k[KPS]0.98[MPC]1.9. The presence of alkaline metal halides accelerated the polymerization. The larger the radius of metal cation or halide ion was, the larger the accelerating effect was. The accelerating salt effect was explained by interactions of salt ions with ionic moieties of the propagating polymer radical and/or the MPC monomer. A kinetic study was also performed on the polymerization of MPC with KPS in water in the presence of NaCl of 2.5 mol/l. Rp at 40 °C was expressed by Rp = k[KPS]0.6[MPC]1.6. A very low value of 4.7 kcal/mol was obtained as the overall activation energy of the polymerization. 相似文献