摘要:

AbstractComputational quantum chemistry has advanced over the past two decades to the point of recognition as a valuable co‐laborer with experiment. Several examples demonstrate this point. For each of the next 40 years, we predict that an additional 1% of chemical research will shift from experiment to computation. Thus by the year 2036 we foresee a picture of chemical research in which 50% of the effort is computational in natur

ISSN:0009-4536    

DOI:10.1002/jccs.199600017

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe irradiation of 2,3‐bis(tert‐butylsulfonyl)norbornadiene (5) and 2‐(tert‐butylsulfonyl)norbornadiene (6) yielded the expected quadricyclane derivatives as stable molecules. The irradiation of 2,3‐bis(tert‐butylsulfonyl)bicyclo[2.2.2]octa‐2,5‐diene(7) 2,3‐bis(tert‐butylsulfonyl)‐exo‐7,8‐epoxybicyclo[2.2.2]‐octa‐2,5‐diene (8) and 8,9‐bis(tert‐butylsulfonyl)‐4‐anti‐phenyl‐3,5‐dioxa‐exo‐tricyclo[5.2.2.02,6] undeca‐8,10‐diene 9a and itssyn‐isomer 9b yielded the corresponding tetracyclic and pentacyclic systems, respectively. The photoproducts of 8 and 9 reverted to the starting products slowly at room temperature. The half‐life of the photoproduct of 7 was determined to be 34 min at 50 °C. Compound 9a reacted with

ISSN:0009-4536    

DOI:10.1002/jccs.199600018

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe nonlinear absorption and refraction of soluble phthalocyanines and naphthalocyanines have been measured with z‐scan technique using 8 ns, 532 nm laser pulses. The excited‐state absorption cross‐section and the excited‐state refractive‐index cross section have been estimated under the consideration of laser induced thermal effect. The excited state absorption induced n2and Re χ(3)values are in the range of 10−12esu. These observed data are enhanced by the concentrations of both metal substituted Pc's and Nc's, but this increment became very small for the metal free phthalocyanine. During the optical limiting experiments, a 25% linear transmitted solution of R8PcH2can limit laser pulses to ≤ 120 μJ from incident energies as high as 2.0 mJ, and this limitation moved down to ≤ 50 μJ when replacing R8PcCu from P8PcH2. A similar property has also been observed for the metal substituted naphthalocyanines. The results indicate that both the nonlinear refraction and optical limiting properties should be strongly affected by the metal induced triplet‐state nonlinear absorption in both Pc's and Nc's. Moreover, the laser pulses created a self trapped filament inside the solution of this optical limiter, while emitting time‐resolved, concentric rings on a projection screen, which could be induced by the thermal lensing effect. The various optical nonlinear properties observed from these materials should make them valuable

ISSN:0009-4536    

DOI:10.1002/jccs.199600019

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractNew ferroelectric liquid crystals containing two chiral centers, 4‐(4′‐n‐alkyloxyphenyl)phenyl 4‐{2(S)‐[2(S)‐methylbutyloxy]propoxy}benzoate (4a‐4f) and4‐(n‐alkyloxy)phenyl 4‐{4′‐[2(S)‐(2(S)‐methylbutyloxy)propoxy]phenyl}benzoate (5a‐5f) were synthesized and their physical properties studied. A phase‐transition sequence ofC‐Sc*‐N*‐Iwas observed in most cases. Some homologues of them,4a‐4d, possess monotropicSc* phase. Not only theSc* phase‐transition temperature of5a‐5fis lower than that of the corresponding4a‐4f, but theirSc* phase‐transition temperature range is also wider than the corresponding4a‐4f. TheSc* phase temperature range can be up to 48 °C. The spontaneous polarization of 8‐28 nC/cm2and the elect

ISSN:0009-4536    

DOI:10.1002/jccs.199600020

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe synthesis of bulk Y2Ba4Cu7O15‐δsuperconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y2Ba4Cu7O15‐δphase. A time‐temperature profile characterizing the conditions for the preparation of Y2Ba4Cu7O15‐δphase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X‐ray diffraction, electrical resistivity, iodometric titration and magnetization measurements

ISSN:0009-4536    

DOI:10.1002/jccs.199600021

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe power of the angle‐resolved ion desorption technique for straightforward characterization of surfaces is demonstrated. The structural sensitivity of secondary ion desorption has led to a successful application of angle‐resolved ion sputtering yield measurements to the determination of the Cl chemical bonding structure on the Ag {100} surface. Angular distributions of the sputtered Cl−ions show that chlorine dissociates at the surface to yield a bonding state of atomic form at the room temperature. Both the polar and the azimuthal angle dependencies of the sputter intensity for Ag+and Cl−ions reveal that the Cl adatom is chemi‐sorbed high above the topmost substrate layer of Ag atoms. At all Cl exposures, the Ag‐Cl bond is oriented along theazimuth with the adsorbate occupying a C4symmetry site, not an a‐top, a bridge, or a high symmetry site. Shadow‐cone enhanced ion desorption spectra show that die geometrical structure of the Cl chemisorbed surface changes slightly as the exposu

ISSN:0009-4536    

DOI:10.1002/jccs.199600022

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe dehydroxylation and rehydroxylation properties of titania (Degussa P‐25) were investigated. FTIR and TPD‐MS data indicate that hydroxyl groups are not completely removed at 500 °Cin vacuo, and rehydration/rehydroxylation occur under helium (water content<1 ppm) flow at room temperature. In addition, repeating dehydroxylation/rehydroxylation treatments for ten times does not significantly modify the dehydroxylation/rehydroxylation property of titania surface. Desorption of hydrogen from titania was observed at 535 °C after titania was reduced above 400 °C. The maximum surface density of hydrogen was determined to be 0.75 H atom/nm2. TPD data show four types of hydrogen on 3% titania supported cobalt catalysts: hydrogen adsorbed on cobalt metal (desorption temperature around 100 °C), reverse spillover hydro gen (150‐250 °C), hydrogen from H‐TiO2‐x‐ Co interacting species (‐330 °C), and recombined hydrogen from Ti3+‐H on titania (‐535 °C). The absence of hydrogen desorption peak at 535 °C for titania supported cobalt reduced above 400 °C can be explained in terms of the migration of H‐TiO2‐xmoieties onto cobalt metal surface during reduction. Removal of hydroxyl groups by thermal treatment before reduction enhanced the amount of hydrogen desorption from normal cobalt surface. This indicates that the hydroxyl groups play a role in th

ISSN:0009-4536    

DOI:10.1002/jccs.199600023

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractOptimized experimental procedures including time of extraction, extraction solvent in Soxhlet extraction technique were sought for detection of trace ethion residues in soil. The largest recoveries over 96% were achieved with a 1:1 mixture of methanol and acetone as extraction solvent for three hours. In comparing EI, CI, EI‐CAD, and PCI‐CAD modes of a four sector mass spectrometry for detection ethion, it was shown the best monitoring mode to be EI monitoring of the M+of ethion,m/z384, which fragments to give them/z231 product ion. The limit of detection obtained was 170 pg/g in s

ISSN:0009-4536    

DOI:10.1002/jccs.199600024

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractChemical investigation of the ethanolic extract ofJasminum polyanthumFranch has resulted in the isolation of verbascoside (10) and 9 secoiridoid glycosides including oleoside dimethyl ester (1), 10‐hydroxy oleoside dimethyl ester (2), oleoside 11 methyl ester (3), methyl‐glucooleoside (4), 8‐epikingiside (5), ligustroside (6), angustifolioside B (7), oleuropein (8), and oleoacetoside (9). The structures of 1‐10 were established primarily on the basis of NMR a

ISSN:0009-4536    

DOI:10.1002/jccs.199600025

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractSeveral novel tetraacetal oxa‐cage compounds9a‐9fwere synthesized from the corresponding 2‐methylthiofuransla‐lfby a short sequence. The structures of these tetraoxa‐cage compounds were deduced from their spectral data and proven by X‐ray analysis of9a. Ozonolysis of theendoadducts5a‐5fin CH2C12at −78 °C followed by reduction with dimethyl sulfide gave the tetraoxa‐cages9a‐9fin 65‐75% yields, respectively. Ozonolysis of the exo adduct6aunder the same reaction conditions gave the tetracarbonyl compound10. The phenylthio group substituted tetraoxa‐cage 13 and the tetraacetal oxa‐cage 17, with one more carbon atom on the apex position, were also synthes

ISSN:0009-4536    

DOI:10.1002/jccs.199600026

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY