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121.
[reaction: see text] Hydrozirconation of alkynes followed by in situ transmetalation to dimethylzinc and 1,2-addition to activated ketones and N-diphenylphosphinoylimines leads to tertiary allylic alcohols and amines in high overall yield. With 8-phenylmenthol as the chiral auxiliary, si-face attack proceeds in good to excellent diastereoselectivities. 相似文献
122.
Peter C. Cherry Derek N. Evans Christopher E. Newall Nigel S. Watson Peter Murray-Rust Judith Murray-Rust 《Tetrahedron letters》1980,21(6):561-564
1,4-Addition of sulphur nucleophiles to the diene () derived the pen-2-em () from clavulanic acid provides the thiadeoxa analogues (–). X-ray analysis of the ester () shows the thermodynamically stable isomers to have the same relative stereochemistry as clavulanic acid. 相似文献
123.
The field ionization (FI) mass spectra of n-heptanal and a series of deuterium labeled analogs have been studied, with the objectives of initiating systematic investigations of reaction mechanisms of FI produced ions and to permit comprison with those found for other ionization processes. It is now recognized that FI ions have: (a) lower average internal energies and (b) shorter residence times than similar ions generated by electron-impact (EI), and the possibility exists of H/D-randomization occuring in ions formed by desorption from the emitter, by unimolecular decomposition close to the emitter and by either ‘fast’ or ‘slow’ metastable decompositions. In this study only the peak shifts of normal ions could be utilized; accurate mass measurements of all major ions revealed elemental compositions similar to EI. A site-specific McLafferty rearrangement gave the base peak at m/e 44 ([C2H4O]+.), although the apparently complementary ion at m/e 70 ([C5H10]+.) arose in a less specific process. Ions at m/e 43 ([C3H7]+) and 71 ([C5H11]+ 80%; [C4H7O]+ 20%) were apparantly generated without significant H/D-scrambling. Of special interest was the observation of the rearrangement ion at m/e 86 ([C5H10O]+.) caused by loss of C-2 and C-3 as C2H4, as found for EI. It is concluded that at least in this system, decomposing molecular ions formed: (a) in the gas phase extremely close to the emitter and/or (b) on the emitter surface, have lifetimes sufficiently short to preclude complete H/D randomization. The results also provide evidence for common fragmentation mechanisms for heptanal molecular ions at both the low end and the high end of the energy distribution. 相似文献
124.
Qijin Chi Wolfgang Göpel Tautgirdas Ruzgas Lo Gorton Peter Heiduschka 《Electroanalysis》1997,9(5):357-365
The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed. 相似文献
125.
Razak J. Al-Essa Richard J. Puddephatt Charles F.H. Tipper Peter J. Thompson 《Journal of organometallic chemistry》1978,157(2):C40-C42
The platinacyclobutane complexes PtCl2L2(C3H5Me)], L pyridine, CD3CN, or tetrahydrofuran, exist as mixtures of isomers containing PH2 or P groups in rapid equilibrium. Decomposition occurs in some cases to give [PtCl2L(CH3CH2CHCH2)]. Stereospecific skeletal isomerisation also occurs in metallocyclobutanes containing the groups PH2 PHR, when R aryl further decomposition gives ν-allylplatinum complexes. 相似文献
126.
Hans-Gerd Janssen Henri M. J. Snijders Jacques A. Rijks Carel A. Crarners Peter J. Schoenmakers 《Journal of separation science》1991,14(7):438-445
The effects of the pressure drop across the column on retention and efficiency in SFC have been studied. Numerical methods are described which enable the prediction of hold-up time and pressure drop in both packed and open tubular columns. Predictions of both hold-up time and pressure drop are in good agreement with experimental data. The density gradient along the column can be calculated using the numerical methods and a procedure is described which enables the calculation of the overall capacity factors of the solutes from the density profile in the column. Significant variations of the capacity factor are observed along the column. The effect of the density gradient along the column on local diffusivity and dispersion is studied. The column efficiency in systems with significant pressure drops is affected by changes in: the linear velocity of the mobile phase; the diffusion coefficients; and the capacity factors of the solutes along the column. The overall efficiency of the chromatographic system can be calculated if, as is the case for open tubular columns, adequate plate height equations are available. 相似文献
127.
Kadhim H. Al-Obaidi Robert D. Gillard Leon A. P. Kane-Maguire Peter A. Williams 《Transition Metal Chemistry》1977,2(1):64-66
Summary Bis-(5-nitro-1,10-phenanthroline)platinum(II) dichloride and diperchlorate have been prepared. The reaction between the parent cation and hydroxide ion has been studied using 1 FI n.m.r. spectroscopy and found to involve attack at the ligand. The bis-(2,2-bipyridyl)platinum(II) ion has been shown to be highly reactive towards methoxide ion. The dissociation of a 2,2-bipyridyl ligand is preceded by attack at the ligand.Part XI: R. D. Gillard, t.. A. P. Kane-Maguire and P. A. Williams,Transition Met. Chem., 2, 47 (1977).On leave from the University of Baghdad, Iraq. 相似文献
128.
Peter Brown 《Journal of mass spectrometry : JMS》1970,3(5):639-646
The [M]+˙ → [M ? Cl]+ reaction in a series of m- and p-X substituted chlorobenzenes has been studied, utilizing a simple kinetic approach, comparison of metastable ion relative abundances, and by measurement of ionization and appearance potentials. All evidence obtained is consistent with rearrangement prior to cleavage in the molecular ions, in which substituent position becomes effectively randomized. These findings are related to known hydrogen randomization reactions occurring in either the molecular ion or [M ? Cl] ion of chlorobenzenes. Mechanisms involving carbon scrambling via such species as ionized benzvalenes or prismanes, or ring-opening to isomeric acyclic molecular ions in which hydrogen randomization might occur can be entertained, but mechanisms involving simple hydrogen shifts in the intact benzene ring appear less likely. 相似文献
129.
Martin R. Bryce Peter J. Skabara Adrian J. Moore Andrei S. Batsanov Judith A.K. Howard Vanessa J. Hoy 《Tetrahedron》1997,53(52):1002-17794
Reactions of tetrathiafulvalenyllithium (TTF-Li) with a range of aldehydes and ketones have been explored for the first time, to provide an efficient route to mono-functionalised TTF derivatives of general formulae TTF-CH(OH)R (R = alkyl, phenyl, tetrathiafulvalenyl and ferrocenyl) and TTF-CR(OH)R′ (R = alkyl, phenyl, R′ = alkyl, phenyl, tetrathiafulvalenyl, ferrocenyl, and R-R′ = fluorenyl). Subsequent transformations involving the reactive alcohol group of some of these compounds are reported. The structures of the three title compounds have been established by single-crystal X-ray analysis. 相似文献
130.
Peter Ettmayer Walter Schebesta Alfred Vendl Richard Kieffer 《Monatshefte für Chemie / Chemical Monthly》1978,109(4):929-941
The System V–Cr–N has been investigated at 1100 and 1400 °C and at nitrogen pressures between 1 and 1000 atmospheres by X-ray techniques. VN and CrN on the one hand and V2N and Cr2N on the other are forming complete series of solid solutions. The phase field of the mononitride solid solution is dependent on nitrogen pressure and temperature conditions.
Auszug aus der Diplomarbeit des Herrn Dipl.-Ing. Dr.W. Schebesta. 相似文献
Auszug aus der Diplomarbeit des Herrn Dipl.-Ing. Dr.W. Schebesta. 相似文献