A single Br/Mg exchange of 1,2-dibromocyclopentene with iPrMgCl LiCl provides the corresponding beta-bromocyclopentenylmagnesium reagent, which can then be reacted with various electrophiles (yields: 65-82 %). In the presence of a secondary alkylmagnesium halide and Li2CuCl4 (2 mol %), these 2-bromoalkenylmagnesium compounds undergo bromine substitution and can then further react with electrophiles to give 1,2-difunctionalised cyclopentenes (63-79 %). The mechanism of this process is discussed. 相似文献
Applying optimal control to photoinduced trans-cis isomerization in condensed phase, the dynamics of bond-twisting motion of 1,1'-diethyl-4,4'-cyanine in methanol and propanol is revealed. The shape of the optimized pulse resulting from minimization of the photoisomer formation can be directly related to the initial excited-state dynamics in close proximity to the Franck-Condon point. The solvent viscosity-dependent ultrafast wavepacket motion is reflected in the prominent down-chirp of the optimized pulses and reveals a detailed picture of the control mechanism: The reduction of the isomer production is achieved by most efficient dumping of excited population back to the trans ground state. In the higher-viscosity solvent, propanol, wavelength-dependent oscillatory features are superimposed to the overall chirp structure pointing to the importance of excited-state vibrational coherences for the dumping process. 相似文献
Using optimal control as a spectroscopic tool we decipher the details of the molecular dynamics of the essential multidimensional excited-state photoisomerization - a fundamental chemical reaction of key importance in biology. Two distinct nuclear motions are identified in addition to the overall bond-twisting motion: Initially, the reaction is dominated by motion perpendicular to the torsion coordinate. At later times, a second optically active vibration drives the system along the reaction path to the bottom of the excited-state potential. The time scales of the wavepacket motion on a different part of the excited-state potential are detailed by pump-shaped dump optimal control. This technique offers new means to control a chemical reaction far from the Franck-Condon point of absorption and to map details of excited-state reaction pathways revealing unique insights into the underlying reaction mechanism. 相似文献
Summary: The thermodynamic equilibrium in a melt of homopolymer C mixed with clay modified by a diblock copolymer AB is considered in theory. It is assumed that mixing is carried out in two stages. At first, the diblock copolymer penetrates into the interlayers formed by long clay sheets. Then, the clay with adsorbed diblock copolymer chains is added to the homopolymer melt. It is shown that the first process is thermodynamically favorable only if the interlayer width exceeds some threshold value that depends mostly on the difference in the adsorption energy of units A and B. A spontaneous mixing at the second stage is possible only if the enthalpic interactions between homopolymer and copolymer units are not very unfavorable. If so, the formation of an intercalated state is expected for a homopolymer of length comparable to the copolymer length, while for a long homopolymer the anticipated equilibrium state is exfoliation. The spatial distribution of A, B, and C units across the interlayer has been studied for different parameters of the system. The most readily adsorbing units A occupy almost all clay surface. However, the layer of block A is considerably swelled by both B and C units. The mutual distribution of units B and C may vary from almost homogeneous to having rather sharp boundary depending on the value of the Flory‐Huggins parameter χBC. The formation of a pure homopolymer layer at the center of the interlayer indicates about a tendency to exfoliate.
Interlayer profiles of the fractions of units A, B, and C, respectively. 相似文献
LetT be a weakly almost periodic (WAP) representation of a locally compact Σ-compact groupG by linear operators in a Banach spaceX, and letM = M(T) be its ergodic projection onto the space of fixed points (i.e.,Mx is the unique fixed point in the closed convex hull of the orbit ofx). A sequence of probabilities Μn is said toaverage T [weakly] if ∫T(t)x dΜn converges [weakly] toM(T)x for eachx ∃X. We callΜn [weakly]unitarily averaging if it averages [weakly] every unitary representation in a Hilbert space, and [weakly]WAPRaveraging if it averages [weakly] every WAP representation. We investigate some of the relationships of these notions, and connect
them with properties of the regular representation (by translations) in the spaceWAP(G).
Research partially supported by the Israel Science Foundation. 相似文献
The influence of energetic parameters of the interchain homo- and heterocontacts on a local ordering of Bernoullian copolymers has been studied using Monte Carlo simulations and probabilistic analysis. The results of both methods are in a good agreement. Then simple Monte Carlo procedure was employed to study the ordering in products of a polymeranalogous reaction with accelerating effect of neighboring groups. When the reaction with intra- and interchain acceleration and local ordering proceed simultaneously in confined conditions, the ordering might affect the process so that the formation of certain nano-structures (in particular, not trivial strip-like ones) is possible. 相似文献
Nitrosyl fluoride and nitrosyl chloride are crystallized from the melt. The crystal structures are made up by ON–F and ON–Cl molecules with only weak intermolecular interactions. ON–F: a = 411.0(2), b = 439.1(2), c = 1020.2(4) pm, space group P212121. ON–Cl: a = 1084.0(2), b = 543.5(1), c = 409.3(1) pm, space group Pnma. Both molecules have considerable longer nitrogen‐halogen bonds and shorter nitrogen‐oxygen bonds in the solid than in the gaseous state. These differences between gas and solid state structure are expressed much stronger in ON–Cl than in ON–F. ON–F functions as a solvate molecule in the cation of NO+(NOF)2IF8–. Here the ON–F molecule has a drastically shortened NO and lengthened NF bond. NO+(NOF)2IF8–: a = 618.9(1), b = 1039.4(1), c = 2842.1(1) pm, space group P212121. 相似文献