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191.
Three kinds of polar substitutent effects are observable in the solvolyses of 1-R-substituted 3-bromoadamantanes (VI). This follows from the relationship between products, rate constants k in 80% ethanol, and the inductive substituent constants σ of the substituent R. Alkyl groups and electron-attracting substituents at C (1) control the rate by their inductive effects alone, since logk correlates closely with σ. However, rates are higher than predicted on the basis of the respective σ values when conjugating (+ M)-substituents or electrofugal groups are attached to C(1). These exalted substituent effects are attributed to CC-hyperconjugative relay of positive charge from the cationic center at C(3) to the substituent at C(1). When the substituent is a strong electron donor (e.g. O? and S?), accelerated substitution gives way to heterolytic fragmentation, rates and products then being controlled by the frangomeric effect. 相似文献
192.
The unstrained 3-chloroalcohols 1a , 2a and 3a do not undergo solvolytic fragmentation in neutral and weakly acidic 80% ethanol, only substitution and elimination products being formed by the limiting SN1-E1 mechanisms. This also applies to the corresponding ethers 1b and 3b . Addition of sodium hydroxide causes the observed rate constants for the 3-chloroalcohols to rise steeply by factors of at least 103 to 105. These level off at higher base concentrations due to an opposing ionic strength effect. Whereas 3a fragments quantitatively in the presence of base, 1a and 2a fragment in competition with elimination to the Δ3-olefins 9a and 10 , respectively. 2a also yields 2% of the oxetane 6b . These results support a concerted base-induced fragmentation mechanism which competes with intramolecular base-induced elimination (Ei) in the case of the acyclic chloroalcohols 1a and 2a . The formation of small amounts of the oxetane 6b from 2a is attributed to intramolecular nucleophilic substitution at the tertiary carbon atom. 相似文献
193.
The solvolysis rates and products of the 2-exo- norbornyl, bicyclo[3.2.1]oct-8-yl, bicyclo[3.3.1]non-2-yl, bicyclo[3.2.1]oct-6-yl, bicyclo[3.2.1]oct-2-yl and bicyclo[3.2.2]non-6-yl p-toluenesulfonates 10–15 , respectively, are reported. The exo/endo rate ratios for these epimeric secondary tosylates in 80% EtOH varied from 1125 for 11 to 1.6 for 15 . The relative rates varied between 2278 for exo- 10 and 4 ·10?3 for endo- 11 . The hydrolysis products were mainly rearranged alcohols and olefins. The unrearranged alcohols from the exo-tosylates were formed with complete or predominant retention of configuration, whereas those derived from the endo-tosylates were mostly inverted. These results confirm the hypothesis that relative rates, as well as products, are largely determined by the degree of bridging between the cationic center and a dorsal C-atom in the transition state and in the resulting ion pairs. Since bridging is a directed bonding interaction, it is subject to the same angle and conformational strains as ordinary covalent bonds. But bridging requires less geometrical change than the formation of normal bonds and of nonclassical ions. 相似文献
194.
Dr. Xiaojiao Yuan Dr. Kunran Yang Dr. Chloé Grazon Dr. Cong Wang Dr. Lorenzo Vallan Jean-David Isasa Dr. Pedro M. Resende Dr. Fanxing Li Dr. Cyril Brochon Dr. Hynd Remita Dr. Georges Hadziioannou Dr. Eric Cloutet Dr. Jian Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(1):e202315333
Organic π-conjugated semiconductors (OCSs) have recently emerged as a promising alternative to traditional inorganic materials for photocatalysis. However, the aggregation of OCSs in photocatalytic aqueous solution caused by self-assembly, which closely relates to the photocatalytic activity, has not yet been studied. Here, the relationship between the aggregation of 4,7-Bis(thiophen-2-yl) benzothiadiazole (TBT) and the photocatalytic activity was systematically investigated by introducing and varying the position of methyl side chains on the two peripheral thiophene units. Experimental and theoretical results indicated that the introduction of -CH3 group at the 3-position of TBT resulted in the smallest size and best crystallinity of aggregates compared to that of TBT, 4- and 5-positions. As a result, TBT-3 exhibited an excellent photocatalytic activity towards H2 evolution, ascribed to the shorten charge carrier transport distance and solid long-range order. These results suggest the important role of aggregation behavior of OCSs for efficient photocatalysis. 相似文献
195.
Benoit Deprez Damien Bosc Julie Charton Cyril Couturier Rebecca Deprez-Poulain Marion Flipo Florence Leroux Baptiste Villemagne Nicolas Willand 《Molecules (Basel, Switzerland)》2021,26(19)
Chemical biology and drug discovery are two scientific activities that pursue different goals but complement each other. The former is an interventional science that aims at understanding living systems through the modulation of its molecular components with compounds designed for this purpose. The latter is the art of designing drug candidates, i.e., molecules that act on selected molecular components of human beings and display, as a candidate treatment, the best reachable risk benefit ratio. In chemical biology, the compound is the means to understand biology, whereas in drug discovery, the compound is the goal. The toolbox they share includes biological and chemical analytic technologies, cell and whole-body imaging, and exploring the chemical space through state-of-the-art design and synthesis tools. In this article, we examine several tools shared by drug discovery and chemical biology through selected examples taken from research projects conducted in our institute in the last decade. These examples illustrate the design of chemical probes and tools to identify and validate new targets, to quantify target engagement in vitro and in vivo, to discover hits and to optimize pharmacokinetic properties with the control of compound concentration both spatially and temporally in the various biophases of a biological system. 相似文献
196.
197.
Cyril Houdayer 《Journal of Functional Analysis》2007,242(2):375-399
We give in this paper a new construction of factors of type III1. Under certain assumptions, we can, thanks to a result by Popa, give a complete classification for this family of factors. Although these factors are never full, we can nevertheless, in many cases, compute Connes' τ invariant. We obtain a new example of an uncountable family of pairwise non-isomorphic factors of type III1 with the same τ invariant. 相似文献
198.
This study deals with continuous limits of interacting one-dimensional diffusive systems, arising from stochastic distortions
of discrete curves with various kinds of coding representations. These systems are essentially of a reaction-diffusion nature.
In the non-reversible case, the invariant measure has in general a non Gibbs form. The corresponding steady-state regime is
analyzed in detail, by using a tagged particle together with a state-graph cycle expansion of the probability currents. As
a consequence, the constants appearing in Lotka–Volterra equations—which describe the fluid limits of stationary states—can
be traced back directly at the discrete level to tagged particle cycles coefficients. Current fluctuations are also studied
and the Lagrangian is obtained via an iterative scheme. The related Hamilton–Jacobi equation, which leads to the large deviation
functional, is investigated and solved in the reversible case, just for the sake of checking. 相似文献
199.
We construct a Markov family of solutions for the 3D Navier-Stokes equations perturbed by a non degenerate noise. We improve
the result of [3] in two directions. We see that in fact not only a transition semigroup but a Markov family of solutions
can be constructed. Moreover, we consider a state dependant noise. Another feature of this work is that we greatly simplify
the proofs of [3].
Dedicated to Giuseppe Da Prato on the occasion of his 70th birthday 相似文献
200.
A non-empty word w is a Lyndon word if and only if it is strictly smaller for the lexicographical order than any of its proper suffixes. Such a word w is either a letter or admits a standard factorization uv where v is its smallest proper suffix. For any Lyndon word v, we show that the set of Lyndon words having v as right factor of the standard factorization is regular and compute explicitly the associated generating function. Next, considering the Lyndon words of length n over a two-letter alphabet, we establish that, for the uniform distribution, the average length of the right factor v of the standard factorization is asymptotically 3n/4. 相似文献