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21.
N. R. Lerner 《Journal of polymer science. Part A, Polymer chemistry》1974,12(11):2477-2495
The free radicals in p-polyphenylene and the formation of free radicals in this polymer upon pyrolysis in vacuum have been studied by means of electron spin resonance. For an unpyrolyzed series of polymer samples, a linear relationship was observed between free radical concentration and increasing carbon content. The free radicals observed in the unpyrolyzed samples did not react with NO. When samples of polyphenylene were pyrolyzed, additional free radicals were produced which did react with NO. The growth of free radical concentration upon pyrolysis was observed to be closely related to the production of volatile products from the polymer. In the temperature range 250–600°C, HCl was the principal volatile species produced. Two mechanisms were involved in HCl production: a process with an activation energy of 7.1 kcal/mole which led to the production of stable free radicals; and a process involving 75 kcal/mole which was unconnected with the production of free radicals. From 600 to 700°C, H2 was the principal volatile degradation product. The rate at which H2 was evolved showed a second-order dependence on phenyl units bearing two or three substituents; this process had an activation energy of 79 kcal/mole. Electron spin resonance spectra indicated that this process led to the production of free radicals, and infrared spectra showed that a highly crosslinked product resulted. 相似文献
22.
KANG Yong-Feng LIU Lei YAN Wen-Jin XU Zhao-Qing ZHOU Yi-Feng HAN Zhi-Jian NI Ming DA Chao-Shan WANG Rui 《有机化学》2004,24(Z1):163
Development of new or improved methods for the asymmetric preparation of chiral propargylic alcohols has gained considerable significance during the past years because they are useful building blocks for the synthesis of many biologically active compounds and natural products.[1] A series of chiral tridentate ligands were conveniently synthesized from amino acids with good yields (Scheme 1).[2] A preliminary study of the enantioselective alkynylation of benzaldehyde catalyzed by this chiral tridentate ligand was carried out and up to 83% ee of chiral propargyl alcohols was obtained (Table 1 ). A further investigation of the tridentate ligand is currently underway. 相似文献
23.
In the thermolysis of the silaterazolines silatetrazoline tBu2SiNSiCltBu2 · tBu3SiN3 the silanimine tBu2SiNSiCltBu2 and the silyl azide tBu3SiN3 are formed quantitatively. The silanimine tBu2SiNSiCltBu2 has been trapped with Et3NHF, Me3NHCl, water, 1-butene, 2,3-dimethyl-1,3-butadiene, isobutene, methylvinyl ether, and tBu2SiClN3. The structure of the disiloxane (tBu2SiCl-NH-SitBu2)2O and of the bis(di-tert-butylchlorsilyl)-substituted silatetrazoline tBu2SiNSiCltBu2 · tBu2SiClN3 has been determined by X-ray structure analysis. 相似文献
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25.
C. M. Lerner Y. P. Ma J. S. Brooks R. Messervey P. Tedrow 《Applied Physics A: Materials Science & Processing》1991,52(6):433-437
The longitudinal and transverse magnetoresistance to fields of 19 Tesla and 4.2 K has been measured for bismuth films ranging in thickness from 0.01 to 2 m. We have observed a pronounced maximum in the longitudinal magnetoresistance which is thickness dependent. We compare these results with classical size effect theories for the longitudinal magnetoresistance in terms of magnetic-field-dependent electron scattering at grain and film boundaries. Measurements of the longitudinal magnetoresistance to 38 Tesla show a quenching of the classical size effect in the high field limit. This result strongly supports our analysis.Work supported by NSF grant #DMR 8113456Supported by the National Science Foundation 相似文献
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27.
Lozhkomoev A. S. Bakina O. V. Glazkova E. A. Svarovskaya N. V. Lerner M. I. 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(12):2530-2534
Russian Journal of Physical Chemistry A - Porous composites of different phase composition are synthesized via oxidation in a water–ethanol mixture of bimetallic Al/Zn nanoparticles obtained... 相似文献
28.
Wei Xu Dr. Karoly Kozma Tianxiang Sha Yi-Jen Wu Prof. May Nyman Prof. Michael M. Lerner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(36):8101-8104
The alkaline earth metals (M=Mg, Ca, Sr, and Ba) exhibit a +2 oxidation state in nearly all known stable compounds, but MI dimeric complexes with M−M bonding, [M2(en)2]2+, (en=ethylenediamine) of all these metals can be stabilized within the galleries of donor-type graphite intercalation compounds (GICs). These metals can also form GICs with more conventional metal (II) ion complexes, [M(en)2]2+. Here, the facile interconversion between dimeric-MI and monomeric-MII intercalates upon the addition/removal of en are reported. Thermogravimetry, powder X-ray diffraction, and pair distribution function analysis of total scattering data support the presence of either [M2(en)2]2+ or [M(en)2]2+ guests. This phase conversion requires coupling graphene and metal redox centers, with associated reversible M−M bond formation within graphene galleries. This chemistry allows the facile isolation of unusual oxidation states, reveals M0→M2+ reaction pathways, and present new opportunities in the design of hybrid conversion/intercalation materials for applications such as charge storage. 相似文献
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30.
为评估基于单矢量水听器的方位估计能力,在黄海海域对矢量水听器进行实验。矢量水听器吊放于接收船尾部,采用平均声强器和复声强器方位估计方法,并提出以概率密度值最大的方位角作为目标方位估计值的具体处理准则,对恒定方向、匀速行驶的目标船方位进行估计,并求出两种方法的方位估计误差。结果表明,水听器布放深度10 m时,对正横距离为0.42 km的航速10 kn的目标船,平均声强器方法的水平方位角估计误差18°,极角估计误差为5°,可以在离目标船最远1.17 km处估计其方位;复声强法的水平方位角估计误差为13°,极角估计误差为8°,可以在离目标船最远2.35 km处估计其方位。在有接收船的噪声干扰情况下,复声强器比平均声强器方法估计的方位更准确,可以对更远处的噪声源进行方位估计。 相似文献