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Thermodynamic Control (thermodynamic + control)
Selected AbstractsTemplate-Directed Syntheses of Rigid Oligorotaxanes under Thermodynamic Control,ANGEWANDTE CHEMIE, Issue 40 2010Matthew E. Belowich Durch strategisches Platzieren von Erkennungsstellen für sekundäre Dialkylammoniumionen im magischen Abstand von 3.5,Å in der Hantelkomponente einer Serie von Oligorotaxanen (siehe Bild) werden andernfalls konformativ flexible [n]Rotaxane starr und stabförmig gemacht. Die Oligorotaxane entstehen mit nahezu quantitativem Umsatz unter thermodynamischer Kontrolle mittels dynamischer kovalenter Chemie. [source] Polycatenation under Thermodynamic Control,ANGEWANDTE CHEMIE, Issue 18 2010Thermodynamisch zum Ziel! Iodid-katalysierte reversible nucleophile Angriffe wurden für die thermodynamisch kontrollierte Synthese von seitenkettensubstituierten Polycatenanen genutzt. Die Catenierungen, die entlang der Polymerkette ablaufen, werden durch die intra- und intermolekularen ,,,,,-Stapelwechselwirkungen zwischen den Seitenketten aufeinanderfolgender Catenane zum vollständigen Umsatz getrieben. [source] Nitro-Substituted Aryl Lithium Compounds in Microreactor Synthesis: Switch between Kinetic and Thermodynamic Control,ANGEWANDTE CHEMIE, Issue 43 2009Aiichiro Nagaki Dr. Beeil Dich oder lass Dir Zeit, je nach dem, was Du willst: Mit einer Mikroflussmethode zur Erzeugung und Umwandlung o -, m - und p -Nitro-substituierter Aryllithiumverbindungen konnte selektiv entweder das kinetisch oder das thermodynamisch begünstigte Intermediat genutzt werden. Im gezeigten Beispiel entstand bei einer Verweildauer von 0.06,s bei ,48,°C 1, während eine Verweildauer von 63,s ausschließlich 2 ergab. [source] Asymmetric Synthesis of Tetrahydrofurans by Competitive [1,2]-Phenylsulfanyl (PhS) Migrations under Thermodynamic Control.CHEMINFORM, Issue 16 2003Lorenzo Caggiano Abstract For Abstract see ChemInform Abstract in Full Text. [source] Template-Directed Synthesis of Multiply Mechanically Interlocked Molecules Under Thermodynamic ControlCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2005Fabio Aricó Dr. Abstract The template-directed construction of crown-ether-like macrocycles around secondary dialkylammonium ions (R2NH2+) has been utilized for the expedient (one-pot) and high-yielding synthesis of a diverse range of mechanically interlocked molecules. The clipping together of appropriately designed dialdehyde and diamine compounds around R2NH2+ -containing dumbbell-shaped components proceeds through the formation, under thermodynamic control, of imine bonds. The reversible nature of this particular reaction confers the benefits of "error-checking" and "proof-reading", which one usually associates with supramolecular chemistry and strict self-assembly processes, upon these wholly molecular systems. Furthermore, these dynamic covalent syntheses exploit the efficient templating effects that the R2NH2+ ions exert on the macrocyclization of the matched dialdehyde and diamine fragments, resulting not only in rapid rates of reaction, but also affording near-quantitative conversion of starting materials into the desired interlocked products. Once assembled, these "dynamic" interlocked compounds can be "fixed" upon reduction of the reversible imine bonds (by using BH3,THF) to give kinetically stable species, a procedure that can be performed in the same reaction vessel as the inital thermodynamically controlled assembly. Isolation and purification of the mechanically interlocked products formed by using this protocol is relatively facile, as no column chromatography is required. Herein, we present the synthesis and characterization of 1) a [2]rotaxane, 2) a [3]rotaxane, 3) a branched [4]rotaxane, 4) a bis [2]rotaxane, and 5) a novel cyclic [4]rotaxane, demonstrating, in incrementally more complex systems, the efficacy of this one-pot strategy for the construction of interlocked molecules. [source] Resolution of Racemic N -Benzyl ,-Amino Acids by Liquid-Liquid Extraction: A Practical Method Using a Lipophilic Chiral Cobalt(III) Salen Complex and Mechanistic StudiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pawel Dzygiel Abstract The efficient resolution of racemic N -benzyl ,-amino acids (N -Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen,cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N -benzyl ,-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII,,,CoII) counter-extraction with aqueous sodium dithionite or L -ascorbic acid in methanol. Thereductive cleavage allowed to recover the [CoII(3)] complex in good yield, which could be easily re-oxidized to[CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N -Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N -benzyl ,-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Preparation, Crystallographic Characterization, and Theoretical Study of C70(CF3)14,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2006Alexey A. Goryunkov Abstract Five C70(CF3)14 isomers have been isolated chromatographically from the mixture produced in the ampoule reaction between C70 and CF3I at 390 °C. Molecular structures of four isomers have been determined in a single-crystal X-ray diffraction study. A quantum chemical survey of the theoretically possible isomers demonstrated that the structures obtained are energetically favorable but that there is probably no full thermodynamic control in the trifluoromethylation process.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Lewis Acid Induced [2+2] Cycloadditions of Silyl Enol Ethers with ,,,-Unsaturated Esters: A DFT AnalysisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2005Manuel Arnó Abstract The Lewis acid (LA) induced cycloaddition of trimethysilyl vinyl ether with methyl acrylate has been studied by DFT methods at the B3LYP/6-31G* level. In the absence of an LA, a [4+2] cycloaddition between the silyl enol ether and methyl acrylate in the s-cis conformation takes place through an asynchronous, concerted bond-formation process. This cycloaddition presents a large activation enthalpy of 21.1 kcal,mol,1. Coordination of the LA AlCl3 to the carbonyl oxygen atom of methyl acrylate yields a change of molecular mechanism from a concerted to a two-step mechanism and produces a drastic reduction of the activation energy. This stepwise mechanism is initialized by the nucleophilic attack of the enol ether at the ,-position of methyl acrylate in a Michael-type addition. The very low activation energy (7.1 kcal,mol,1)associated with this nucleophilic attack can be related to the increase of the electrophilicity of the LA-coordinated ,,,-unsaturated ester, which favors the cycloaddition through a polar process. The subsequent ring-closure allows the formation of the corresponding [2+2] and [4+2] cycloadducts. While the [4+2] cycloadduct is formed by kinetic control, the [2+2] cycloadducts are formed by thermodynamic control. The energetic results provide an explanation for the conversion of [4+2] cycloadducts into the thermodynamically more stable [2+2] ones. The cis/trans ratio found for the catalytic [2+2] process is in agreement with the experimental outcome. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Allosteric activation of pyruvate kinase via NAD+ in rat liver cellsFEBS JOURNAL, Issue 14 2001Anne Devin In isolated rat hepatocytes, it has previously been reported that a rise in the ATP content induces a proportional increase in cytosolic NAD+ concentration [Devin, A., Guérin, B. & Rigoulet, M. (1997) FEBS Lett.410, 329,332]. This occurs under physiological conditions such as various substrates or different energetic states. To investigate the effect of a physiological rise in cytosolic [NAD+] per se on glycolysis and gluconeogenesis, an increase in [NAD+] induced by exogenous nicotinamide addition was obtained without a change in redox potential, ATP/ADP ratio and ATP concentration. Using dihydroxyacetone as substrate, we found that an increase in cytosolic [NAD+] decreases gluconeogenesis and enhances glycolysis without significant alteration of dihydroxyacetone consumption rate. These modifications are the consequence of an allosteric activation of pyruvate kinase via cytosolic NAD+ content. Thus, in addition to the well-known thermodynamic control of glycolysis by pyridine-nucleotide redox status, our study points to a new mechanism of glycolytic flux regulation by NAD+ concentration at the level of pyruvate kinase activity. [source] Theoretical features of macrocyclization equilibria and their application on transacetalation based dynamic librariesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2010Stefano Di Stefano Abstract The theoretical treatment of macrocyclization reactions under thermodynamic control is overviewed in the light of recent growing interest toward Dynamic Combinatorial Chemistry (DCC). The rules governing the equilibrium processes in Dynamic Library (DL) under conditions of perfect mass balance are illustrated. Data related to transacetalation reactions of cyclophane formaldehyde acetals are thoroughly discussed as remarkable examples of systems where experiments and theory make a good match. Copyright © 2010 John Wiley & Sons, Ltd. [source] Theoretical Calculations on the Tetramethyldisilene Rearrangement: A New Approach to an Old Mechanistic ProblemCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009Mrinmoy Nag Dr. Abstract Roark and Peddle first observed that, when not trapped, Me2SiSiMe2 underwent a series of rearrangements to give two major isomeric products: 1,1-dimethyl-1,3-disilacyclobutane and 1,3-dimethyl-1,3-disilacyclobutane. The widely accepted mechanism for this rearrangement was proposed by Barton and co-workers. However, little is known about the thermodynamic or kinetic properties of this reaction, because the relevant data are limited to the product ratios of the two isomers. Our calculations predict that the product ratio is driven by kinetic control rather than thermodynamic control. We also show that new DFT functionals, such as MPW1K and M052X, produce thermochemical results comparable with CCSD(T) calculations. [source] Template-Directed Synthesis of Multiply Mechanically Interlocked Molecules Under Thermodynamic ControlCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2005Fabio Aricó Dr. Abstract The template-directed construction of crown-ether-like macrocycles around secondary dialkylammonium ions (R2NH2+) has been utilized for the expedient (one-pot) and high-yielding synthesis of a diverse range of mechanically interlocked molecules. The clipping together of appropriately designed dialdehyde and diamine compounds around R2NH2+ -containing dumbbell-shaped components proceeds through the formation, under thermodynamic control, of imine bonds. The reversible nature of this particular reaction confers the benefits of "error-checking" and "proof-reading", which one usually associates with supramolecular chemistry and strict self-assembly processes, upon these wholly molecular systems. Furthermore, these dynamic covalent syntheses exploit the efficient templating effects that the R2NH2+ ions exert on the macrocyclization of the matched dialdehyde and diamine fragments, resulting not only in rapid rates of reaction, but also affording near-quantitative conversion of starting materials into the desired interlocked products. Once assembled, these "dynamic" interlocked compounds can be "fixed" upon reduction of the reversible imine bonds (by using BH3,THF) to give kinetically stable species, a procedure that can be performed in the same reaction vessel as the inital thermodynamically controlled assembly. Isolation and purification of the mechanically interlocked products formed by using this protocol is relatively facile, as no column chromatography is required. Herein, we present the synthesis and characterization of 1) a [2]rotaxane, 2) a [3]rotaxane, 3) a branched [4]rotaxane, 4) a bis [2]rotaxane, and 5) a novel cyclic [4]rotaxane, demonstrating, in incrementally more complex systems, the efficacy of this one-pot strategy for the construction of interlocked molecules. [source] Thermodynamic/Kinetic Control in the Isomerization of the [{tBuNP(,-NtBu)}2]2, IonCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004Andrew D. Bond Dr. Abstract The unique structure of [(tBuN)2PK], (2) (containing [(tBuN)2P], monoanions) is in stark contrast to the previously reported Li+ analogue [{[tBuNP(,-NtBu)]2}2]Li4 (1) (containing the dimeric [{tBuNP(,-NtBu)}2]2, ion). DFT and 31P NMR spectroscopic studies reveal that the formation of the monoanion arrangements are most thermodyamically favored for Li, Na, and K, 1 being the product of kinetic control and 2 being the product of thermodynamic control. [source] | ||||||||||||||||||||||