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991.
对于多螺环化合物特别是第二代稠杂螺环树枝状化合物来说,按照IUPAC有关系统命名原则,从螺结构的角度来命名由于太复杂而几乎不可能.本文通过亚基取代途径对第一代螺环结构的简化,方便地系统命名了一种第二代稠杂螺环树枝状化合物.这些六螺化合物可以系统地命名为:1,2,3,4,5,6,7,8,9,10,11,12-十二氢化-2,2:6,6:10,10-三[3,3-二(烷氧羰基)亚环丁-1,1-二甲氧基]苯并[l]菲.通过这一途径,更高代螺环树枝状化合物及其它类型多螺化合物有望可以简单地系统命名. 相似文献
992.
Jacobsson M Oxgaard J Abrahamsson CO Norrby PO Goddard WA Ellervik U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(13):3954-3960
The mechanism for the acid-mediated substitution of a phenolic hydroxyl group with a sulfur nucleophile has been investigated by a combination of experimental and theoretical methods. We conclude that the mechanism is distinctively different in nonpolar solvents (i.e., toluene) compared with polar solvents. The cationic mechanism, proposed for the reaction in polar solvents, is not feasible and the reaction instead proceeds through a multistep mechanism in which the acid (pTsOH) mediates the proton shuffling. From DFT calculations, we found a rate-determining transition state with protonation of the hydroxyl group to generate free water and a tight ion pair between a cationic protonated naphthalene species and a tosylate anion. Kinetic experiments support this mechanism and show that, at moderate concentrations, the reaction is first order with respect to 2-naphthol, n-propanethiol, and p-toluenesulfonic acid (pTsOH). Experimentally determined activation parameters are similar to the calculated values (Delta H exp not equal =105+/-9, Delta H calcd not equal =118 kJ mol(-1); Delta G exp not equal =112+/-18, Delta G calcd not equal =142 kJ mol(-1)). 相似文献
993.
We have designed a new library of readily available, highly modular phosphite-phosphoramidite ligands for asymmetric allylic substitution reactions. They are easily prepared in one step from commercially available chiral 1,2-amino alcohols. The introduction of a phosphoramidite moiety into the ligand design is highly advantageous for the product outcome. This ligand library affords high reaction rates (TOFs of up to 800 mol (mol h)(-1)) and enantioselectivities (ees of up to 99%) and, at the same time, contains a broad range of disubstituted hindered and unhindered substrate types. NMR study of the Pd-pi-allyl intermediates provide a deeper understanding of the effect of the ligand parameters on the origin of enantioselectivity. 相似文献
994.
Carboxymethyl potato starch (CMPS) was synthesized under heterogeneous reaction conditions. The influences of etherification temperature, alkalization and etherification time, sodium hydroxide to monochloroacetic acid (MCA) molar ratio (nNaOH/nMCA), theoretical degree of substitution (DSt), the ratio of isopropyl alcohol (IPA) volume to starch mass (vIPA/mst) on degree of substitution (DS) and reaction efficiency (RE) of CMPS were investigated. Compared with the previous literature data, the results had significant difference for the optimal carboxymethylation conditions of potato starch from different sources. CMPS prepared under optimal conditions showed the highest DS and RE, which were 1.36 and 0.88, respectively. Furthermore, the RE value in this work is considerably higher than that reported in the literature. The time of alkalization and etherification were also discussed independently. In addition, CMPS was characterized by Fourier transform infrared spectrophotometry and scanning electron microscopy (SEM). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
995.
We have theoretically studied the gas‐phase nucleophilic substitution at group‐14 atoms (SN2@A) in the model reactions of Cl?+AH3Cl (A=C, Si, Ge, Sn, and Pb) using relativistic density functional theory (DFT) at ZORA‐OLYP/TZ2P. Firstly, we wish to explore and understand how the reaction coordinate ζ, and potential energy surfaces (PES) along ζ, vary as the center of nucleophilic attack changes from carbon to the heavier group‐14 atoms. Secondly, a comparison between the more common backside reaction (SN2‐b) and the frontside pathway (SN2‐f) is performed. The SN2‐b reaction is found to have a central barrier for A=C, but none for the other group‐14 atoms, A=Si–Pb. Relativistic effects destabilize reactant complexes and transition species by up to 10 kcal mol?1 (for SN2‐f@Pb), but they do not change relative heights of barriers. We also address the nature of the transformation in the frontside SN2‐f reactions in terms of turnstile rotation versus Berry‐pseudorotation mechanism. 相似文献
996.
Debaprasad Mandal Dr. Markus Jurisch Dipl.‐Chem. Crestina S. Consorti Dr. John A. Gladysz Prof. Dr. 《化学:亚洲杂志》2008,3(10):1772-1782
Solutions of the fluorous alkyl halides Rf8(CH2)mX (Rfn=(CF2)n?1CF3; m=2, 3; X=Cl, Br, I) in perfluoromethylcyclohexane or perfluoromethyldecalin are inert towards solid or aqueous NaCl, NaBr, KI, KCN, and NaOAc. However, halide substitution occurs in the presence of fluorous phosphonium salts (Rf8(CH2)2)(Rf6(CH2)2)3P+X? (X=I ( 1 ), Br ( 3 )) and (Rf8(CH2)2)4P+I? (10 mol %), which are soluble in the fluorous solvents under the reaction conditions (76–100 °C). Stoichiometric reactions of a) 1 with Rf8(CH2)2Br and b) 3 with Rf8(CH2)2I were conducted under homogenous conditions in perfluoromethyldecalin at 100 °C and yielded the same Rf8(CH2)2I/Rf8(CH2)2Br equilibrium ratio (≈60:40). This shows that ionic displacements can take place in extremely nonpolar fluorous phases and suggests a classical phase‐transfer mechanism for the catalyzed reactions. Interestingly, the nonfluorous salt (CH3(CH2)11)(CH3(CH2)7)3P+I? ( 4 ) also catalyzes halide substitutions, but under triphasic conditions with 4 suspended between the lower fluorous and upper aqueous layers. NMR experiments established very low solubilities in both phases, which suggests interfacial catalysis. Catalyst 1 is easily recycled, optimally by simple precipitation onto teflon tape. 相似文献
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