Showing papers on "Tetrahydrofuran published in 1986"
TL;DR: An all atom potential energy function for the simulation of proteins and nucleic acids and the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach is presented.
Abstract: We present an all atom potential energy function for the simulation of proteins and nucleic acids. This work is an extension of the CH united atom function recently presented by S.J. Weiner et al. J. Amer. Chem. Soc., 106, 765 (1984). The parameters of our function are based on calculations on ethane, propane, n−butane, dimethyl ether, methyl ethyl ether, tetrahydrofuran, imidazole, indole, deoxyadenosine, base paired dinucleoside phosphates, adenine, guanine, uracil, cytosine, thymine, insulin, and myoglobin. We have also used these parameters to carry out the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach.
3,291 citations
TL;DR: In this article, the synthesis of six alkylammonium salts of the general formula NH+a X−, where R = ethyl, propyl, butyl or sec.−butyl, X− = nitrate or thiocyanate, n is described.
145 citations
TL;DR: In this article, the resonance Raman and infrared spectra of chlorophyll b were observed in various solvents, and the Raman spectra in the 1620-1510-cm/sup -1/ region were classified into two groups, depending on the solvent used.
Abstract: The resonance Raman and infrared spectra of chlorophyll a were observed in various solvents The Raman spectra in the 1620-1510-cm/sup -1/ region were classified into two groups, depending on the solvent used Three Raman bands at 1612-1606 (weak), 1554-1551 (strong), and 1529-1527 (medium) cm/sup -1/ (group I) observed in n-hexane, CCl/sub 4/, CS/sub 2/, diethyl ether, acetone, ethyl acetate, and ethanol solutions shift, respectively, to 1599-1596, 1548-1545, and 1521-1518 cm/sup -1/ (group II) in tetrahydrofuran, dioxane, pyridine, and methanol solutions In the solutions giving rise to the spectrum of group I the Mg atom of chlorophyll a is mostly five-coordinated (with one axial ligand), whereas the six-coordinated species (with two axial ligands) is the major fraction in the solutions giving rise to the spectrum of group II The Raman and infrared spectra of chlorophyll b show that chlorophyll b behaves in the same manner as chlorophyll a with respect to the axial coordination by solvent molecules 22 references, 7 figures
121 citations
TL;DR: The solid silaketimine But2N-SiBut3 has been prepared and structurally characterized [SiN 1.568(3)A, Si-N−Si 177.8(2)°].
Abstract: The pale yellow, solid silaketimine But2N–SiBut3 has been prepared and structurally characterized [SiN 1.568(3)A, Si–N–Si 177.8(2)°]; it forms a stable adduct with tetrahydrofuran by complexation of the unsaturated silicon atom.
103 citations
TL;DR: The reaction of alkyl-and aryl-(dicyclopentadienyl)lutetium complexes with H 2 or D 2 gives dimeric dicyclopsedienyl-hydride or -deuteride.
86 citations
TL;DR: In this article, the reduction of WCl6 or [WCl4(PR2Ph)2](R = Et or Prn) with Mg in the presence of PR2Ph under N2 in tetrahydrofuran (thf) gives a mixture of dinitrogen complexes: [{W(N2)2(PR 2Ph)3}2(µ-N2)](1), trans-[W( N2) 2(PR-2Ph4]4]-(2), and [W(η6
Abstract: Reduction of WCl6 or [WCl4(PR2Ph)2](R = Et or Prn) with Mg in the presence of PR2Ph under N2 in tetrahydrofuran (thf) gives a mixture of dinitrogen complexes: [{W(N2)2(PR2Ph)3}2(µ-N2)](1), trans-[W(N2)2(PR2Ph)4](2), and [W(η6-C6H5PR2)(N2)(PR2Ph)2](3) which can be observed in the 15N n.m.r. spectra of the reaction solutions and isolated in most cases in moderate yield. Compound (1a)(R = Et) is shown to be a dimer by X-ray analysis but the structure could be refined only with constraints on interatomic distances. Compounds (1) react with anhydrous HCl (thf, 20 °C) to give hydrazine (0.2 mol/W atom) and dinitrogen (2 mol/W atom). Compound (2a)(R = Et) crystallises as a thf solvate with W–N = 1.986(6) and 1.994(6), N–N = 1.146(7) and 1.139(7)A. Complex (2a) gives ammonia (1.8 mol/W atom) and N2(1 mol/W atom) on treatment with H2SO4–MeOH. Compound (3b)(R = Prn) has W–N = 1.980(8) and N–N = 1.126(10)A and loses N2 quantitatively on treatment with anhydrous HCl in thf.
80 citations
TL;DR: In this article, the reaction of methyl vinyl ketone with a variety of aldehydes, catalyzed by 1,4-diazabicyclo (2.2) octane (DABCO) in tetrahydrofuran, conveniently provides the corresponding α-methylene-β-hydroxyalkanones in good yields.
78 citations
TL;DR: In this paper, the authors derived ET-values for solutions of LiClO4 in water free diethyl ether, tetrahydrofuran, and 1,2-dimethoxyethane.
Abstract: Fur Losungen von LiClO4 in wasserfreiem Diethylether, Tetrahydrofuran und 1,2-Dimethoyxyethan wurden ET-Werte bestimmt. Als Modellsystem fur die Losungsmittelpolaritat diente die [4 + 2]-Cycloaddition von Acrylsaure-methylester an 1,3-Cyclopentadien.
The Polarity of Solutions of Lithium Perchlorate in Waterfree Ethers
ET-Values were derived for solutions of LiClO4 in waterfree diethyl ether, tetrahydrofuran, and 1,2-dimethoxyethane. The [4 + 2]-cycloaddition of methyl acrylate and 1,3-cyclopentadiene served as model system.
68 citations
TL;DR: In this paper, it is shown that from a solution of a Grignard reagent, C 2 H 5 MgBr (0.5 mol dm −3 ) in THF, it is possible both to electroplate magnesium onto copper and to redissolve it anodically with high coulombic efficiency.
63 citations
TL;DR: In this paper, the condensation of immonium ions with allylsilanes in aqueous tetrahydrofuran at ambient temperature gives rise to five, six, seven, and eight-membered rings containing nitrogen.
55 citations
TL;DR: In this article, the authors investigated the conductivity of LiClO4 and LiPF6 in the mixed systems of the high permittivity solvents and low viscosity (low-viscosity) solutions.
Abstract: Electrolytic conductivities of LiClO4 and LiPF6 have been investigated in the mixed systems of the high permittivity solvents and low viscosity solvents. Propylene carbonate (PC), sulfolane (S), and dimethyl sulfoxide (DMSO) were used as the high permittivity solvents, and 1,2-dimethoxyethane (DME) and tetrahydrofuran (THF) as the low viscosity solvents. The conductivity of 1 mol dm−3 LiClO4 has a miximum in the mixed solvent with 40–80 m/o ether for every system. The conductance improvement by solvent-blending was qualitatively described in terms of a favorable combination of high permittivity and low viscosity of each component. The maximum conductivity of 1 mol dm−3 LiClO4 increased in the order of S
TL;DR: In this paper, a regioselective 1-O -deacetylation of fully acetylated sugars with bis(tributyltin) oxide in toluene at reflux, and with potassium cyanide or potassium hydroxide, or both, in mixtures of tetrahydrofuran and 2-propanol were found to be effective for regiodelective deacetylization of fully-acetylated sugar.
TL;DR: In this paper, liquid squalene, a C/sub 30/H/sub 50/ triterpene, was used in microscale Ag atom experiments as a growth and stabilization medium for Ag colloid, the development of which was monitored by optical spectroscopy.
Abstract: Liquid squalene, a C/sub 30/H/sub 50/ triterpene, a low molecular weight analogue of polyisoprene, was used in microscale Ag atom experiments as a growth and stabilization medium for Ag colloid, the development of which was monitored by optical spectroscopy. For Ag atom depositions with this liquid and a variety of others (e.g., polybutadiene, 1,10-diaza-18-crown-6, 2-methyl tetrahydrofuran), the bandwidth at half-maximum ..delta.. omega/sub 1/2/ and the lambda/sub max/ of the characteristic surface plasmon absorption remained unchanged with increasing amounts of silver, indicative of an unchanging particle size distribution. In other liquids like polyisoprene and poly(dimethylsiloxane-co-methylphenylsiloxane), the surface plasmon ..delta.. omega/sub 1/2/ increased markedly and the lambda/sub max/progressively shifted into the red with increasing amounts of silver atoms signalling the inability of these media to stabilize the initially formed particle size distribution. As a natural extension of this study, liquid-phase agglomeration of metal atoms in various olefinic, aromatic, and ether media was applied to prepare Pd and Ag carbon composites which were used to fabricate electrodes for evaluation of their current/voltage characteristics in the oxygen half-cell of a hydrogen-oxygen fuel cell.
TL;DR: In this article, the results of a least-squares treatment of the equilibrium results were obtained for tetrachloromethane + methanol, + ethanol, + 1-propanol,+ 1-butanol, + 2-methyl-2propanols, + tetrahydrofuran, and + 1,4-dioxane.
TL;DR: Precipitated n-butylpotassium (BuK), prepared by metal exchange between n-butyllithium and potassium-t-amylate, dissolves in hexane after addition of N, N, N ', N '-tetramethylethylenediamine (TMEDA) as discussed by the authors.
TL;DR: Norbornene and norbornadiene have been successfully metallated with the complex BuLi · t-BuOK in tetrahydrofuran and a number of derivatives prepared by reaction of the metallic intermediates with electrophilic reagents.
Abstract: Norbornene and norbornadiene have been successfully metallated with the complex BuLi · t-BuOK in tetrahydrofuran and a number of derivatives prepared by reaction of the metallic intermediates with electrophilic reagents.
TL;DR: In this article, the authors rationalized the results of the SRN1 mechanism in the case of 1 (X = Cl, I ) and showed that the reaction mainly yielded tetrafluoroethylene and 5 instead of 3 and 4.
TL;DR: In this paper, Butyl hydroperoxide and an alkyl-lithium in dry tetrahydrofuran were shown to epoxidise α, β-unsaturated esters and sulphones efficiently in a stereo-and regio-specific manner.
Abstract: t-Butyl hydroperoxide and an alkyl-lithium in dry tetrahydrofuran are shown to epoxidise α,β-unsaturated esters and sulphones efficiently in a stereo- and regio-specific manner, while esters of chiral alcohols undergo diastereofacially selective epoxidation.
TL;DR: In this article, a 1,4-butanediol with heteropoly acids was used for dehydration-cyclization of 1.4-dioxane, where water molecules retard the reaction by hydrating the protons of the acids.
TL;DR: In this paper, it was shown that triruthenium dodecacarbonyl (III) has a (Ru(CO)4)N chain structure and has a high molecular weight.
Abstract: : Irradiation of concentrated solutions of triruthenium dodecacarbonyl (III) in tetrahydrofuran and hydrocarbon solvents under one atmosphere carbon monoxide yields a purple-red compound, IV. Elemental analyses are consistent with IV having the stoichiometry Ru(CO)4, while the very low volatility and solubility in organic solvents suggest that IV has a high molecular weight. Reactions of IV with carbon monoxide, hydrogen, bromine, iodine and carbon tetrachloride essentially duplicate the corresponding reactions of (III), suggesting that the two compounds are isomeric, but reactions of IV with tertiary phosphines yield mononuclea rather than cluster ruthenium compounds. It is there fore proposed that IV has a rather novel, possibly cyclic, structure consisting of (Ru(CO)4)N chains.
TL;DR: In this paper, the crystal structure of compounds IV and V has been solved by X-ray diffraction method, and the results indicated that the tri-m-chlorohexakis(tetrahydrofuran)dimagnesium(II) cation in V is really formed in reaction between [MgCl2(6]2+ cation and [mgCl 2(THF)2]2]-kation.
Abstract: Two [MoOCl3(THF)2] molecules are used for detachment of two Cl atoms from [MgCl2(THF)2]. In such reaction a green crystalline salt [Mg(THF)6][MoOCl4THF]2IV is formed. Compound IV reacts further with 3 equivalents of bis(tetrahydrofuran)magnesium dichloride, yielding a green ionic [Mg2(m-Cl)3(THF)6][MoOCl4THF] compound V. Compound IV and V vary only in a structure of cation what indicated that the tri-m-chlorohexakis(tetrahydrofuran)dimagnesium(II) cation in V is really formed in reaction between [Mg(THF)6]2+ cation and [MgCl2(THF)2]. The crystal structure of compounds IV and V has been solved by X-ray diffraction method. The [Mg(THF)6]2+ cation forms the tetragonally distorted octahedron with the magnesium atom in the symmetry centre. In homobimetallic di-octahedral [Mg2(m-Cl)3(THF)6]+ cation the magnesium atoms are surrounded by three bridging chlorine atoms and three THF molecules. The structures of [MoOCl4THF]− in IV and V are similar. In those anions the molybdenum atom is hexacoordinated with four chlorine atoms in equatorial plane.
Reaktion zwischen [MgCl2(THF)2] und [MoOCl3(THF)2]. Die Kristallstrukturen von [Mg(THF)6] [MoOCl4THF]2 und [Mg2(m-Cl)3(THF)6] [MoOCl4THF]
Zur Entfernung von zwei Chloratomen aus [MgCl2(THF)2] werden zwei [MoOCl3(THF)2]-Molekule benotigt. Diese Reaktion ergibt das grune, kristalline Salz [Mg(THF)6][MoOCl4THF]2IV. Verbindung IV reagiert mit 3 weiteren Aquivalenten Bis(tetrahydrofuran)magnesiumdichlorid, wobei eine grune, ionische Verbindung [Mg2(m-Cl)3(THF)6][MoOCl4THF] V gebildet wird. Beide Verbindungen, IV und V, unterscheiden sich nur in der Struktur des Kations, was darauf hinweist, das das Tris-m-Chlorhexakis(tetrahydrofuran)dimagnesium-Kation V in einer Reaktion zwischen dem [Mg(THF)6]2+-Kation und [MgCl2(THF)2] gebildet wird. Die Kristallstrukturen der Verbindungen IV und V wurden rontgenographisch untersucht. Das [Mg(THF)6]2+-Kation bildet Oktaeder, die tetragonal deformiert sind, wobei sich das Magnesiumatom im Symmetriezentrum befindet. Im homobimetallischen, di-oktaedrischen [Mg2(m-Cl)3(THF)6]-Kation sind die Magnesiumatome von drei bruckenbildenden Chloratomen und drei THF-Molekulen umgeben. Die Struktur von [MoOCl4THF]− in IV ist ahnlich der in V. In diesen Anionen ist das Molybdanatom hexakoordiniert, wobei sich vier Chloratome in der aquatorialen Ebene befinden.
TL;DR: In this paper, a starke Verzogerung der entarteten Cope-Umlagerung im Vergleich zu der 3,7-Dicyansemibullvalens 1a, 1b⇌1b′ bzw.
Abstract: Addition von Trimethylsilylcyanid an das Bicyclo[3.3.0]octan-3,7-dion 8 und nachfolgende Umsetzung der diastereomeren O-silylierten Biscyanhydrine 12 mit Trichlorphosphanoxid in siedendem Pyridin ergibt ein 2:1-Gemisch der regiosiomeren ungesattigten Dinitrile C2-13 und Cs-13. Diese werden mit uberschussigem N-Bromsuccinimid in die Tribrom- (14a) und isomeren Tetrabromdinitrile 14b und 15a ubergefuhrt, die durch Kristallisation und selektive Reaktion von 15a mit Diethylphosphit/Triethylamin getrennt werden. Die Struktur des uberwiegenden, unsymmetrischen Tetrabromdinitrils 15a wird durch eine Rontgenstrukturbestimmung aufgeklart. Zink/Kupfer in siedendem Ether debromiert die Tetrabromdinitrile 14b und 15a glatt zu dem 2,6- (2b) bzw. 2,4-Dibrom-3,7-dicyansemibullvalen 2a. Langeres Erhitzen von 15a mit Zink/Kupfer in Tetrahydrofuran fuhrt dagegen zum Brom-3,7-dicyansemibullvalen 1c⇌1c′. Brom/Lithium-Austausch an 1c⇌1c′ mit tert-Butyllithium bei −100°C und Umsetzung des Lithio-3,7-dicyansemibullvalens 1d mit Methanol, Methan-[D]ol und Dicyan ergeben die Semibullvalene 1a, 1b⇌1b′ bzw. 1e⇌1e′. Die Geschwindigkeit der entarteten Cope-Umlagerung der Dibrom-3,7-dicyansemibullvalene 2a und b wird aus der Austauschverbreiterung von 13C-NMR-Signalen im Bereich von 200–290 K bestimmt. Bei 200 K gilt fur 2ak = 260 s−1, ΔG≠ = 39.1±1.5 kJ·mol−1, fur 2bk = 1160 s−1, ΔG≠ = 36.6±0.6 kJ·mol−1. Die starke Verzogerung der entarteten Cope-Umlagerung im Vergleich zu der des 3,7-Dicyansemibullvalens 1a (k = 1.53·106 s−1, ΔG≠ = 24.6±0.3 kJ·mol−1 bei 200 K) hangt somit nur wenig von der Stellung der Bromatome ab. Die Konstanten K der Valenztautomerie-Gleichgewichte der 3,7-Dicyansemibullvalene 1b⇌1b′ (K = 1.112±0.001 bei 298 K), 1c⇌1c′ (0.065±0.02 bei 300 K), 1e⇌1e′ (0.29±0.02 bei 300 K) und der bekannten Bromsemibullvalene 18⇌18′ (0.2±0.02 bei 300 K) werden aus relativen Temperaturgradienten 13C-chemischer Verschiebungen bzw. mit Hilfe von Saunders' Isotopenstorungs-Methode erhalten. Die durch Rontgenstrukturbestimmung ermittelten Atomabstande der Brom-3,7-dicyansemibullvalene 1c und 2a zeigen, das bei beiden im Kristall keine Cope-Umlagerung stattfindet. Dagegen beobachtet man eine statistische Orientierungsfehlordnung im Kristall des 2,6-Dibrom-3,7-dicyansemibullvalens 2b, die auf eine entartete Cope-Umlagerung im festen Zustand hinweist.
Synthesis, Structure, and Cope Rearrangement of Some 3,7-Dicyano-1,5-dimethylsemibullvalenes
Addition of trimethylsilyl cyanide to the bicyclo[3.3.0]octane-3,7-dione 8 followed by the reaction of the diastereomeric O-silylated biscyanohydrins 12 with phosphoryl chloride in boiling pyridine yields a 2:1 mixture of the regioisomeric unsaturated dinitriles C2-13 and Cs-13. These are converted by an excess of N-bromosuccinimide to the tribromo- (14a) and the isomeric tetrabromodinitriles 14b and 15a which are separated by crystallization and by selective reaction of 15a with diethyl phosphite/triethylamine. The structure of the predominant, unsymmetrical tetrabromodinitrile 15a is determined by an X-ray diffraction analysis. Zinc/copper reagent in boiling ether smoothly debrominates the tetrabromodinitriles 14b and 15a affording the 2,6- (2b) and 2,4-dibromo-3,7-dicyanosemibullvalene 2a, respectively. However, extended heating of 15a in tetrahydrofuran in the presence of zinc/copper reagent produces the bromo-3,7-dicyanoscmibullvalene 1c⇌1c′ Bromine/lithium exchange of the latter by tert-butyllithium at −100°C and quenching of the lithio-3,7-dicyanoscmibullvalene 1d with methanol, methan-[D]ol, and cyanogen yield the semibullvalenes 1a, 1b⇌1b′, and 1e⇌1e′, respectively. The rates of the degenerate Cope rearrangement of the dibromo-3,7-dicyanosemibullvalenes 2a and b are calculated from the exchange broadening of carbon-13 NMR signals in the temperature range 200–290 K. For 200 K one obtains k = 260 s−1, ΔG≠ = 39.1⇌1.5 kJ·mol−1 (2a) and k = 1160 s−1, ΔG≠ = 36.6±0.6 kJ·mol−1 (2b). Thus, the strong deceleration of the degenerate Cope rearrangement relative to that of the 3,7-dicyanosemibullvalene 1a (k = 1.53·106 s−1, ΔG≠ = 24.6±0.3 kJ·mol−1 at 200 K) depends only little on the position of the bromine atoms. For the valence tautomeric equilibria of the 3,7-dicyanosemibullvalenes 1b⇌1b′ (K = 1.112±0.001 at 298 K), 1c⇌1c′ (0.065±0.02 at 300 K), 1e⇌1e′ (0.29±0.02 at 300 K), and the known bromosemibullvalenes 18b⇌18b′ (0.2±0.02 at 300 K) the constants K are determined using relative temperature gradients of carbon-13 shifts or Saunders' isotopic pertubation method. The atomic distances as revealed by X-ray diffraction analyses of the bromo-3,7-dicyanosemibullvalenes 1c and 2a demonstrate that both do not undergo a Cope rearrangement in the crystal. On the contrary, a statistical orientational disorder in the crystal is observed for 2b which is indicative of a degenerate Cope rearrangement in the solid state.
TL;DR: In this article, the reaction of Li[PBut2] with SnCl2 or PbCl2 in tetrahydrofuran (thf) solution affords the isostreuctural "ate" complexes, [Li(thf){E(PBut 2)3}] ], where E = Sn and Pb = Pb.
Abstract: The reaction of Li[PBut2] with SnCl2 or PbCl2 in tetrahydrofuran (thf) solution affords the isostreuctural ‘ate’ complexes, [Li(thf){E(PBut2)3}](E = Sn or Pb), both of which have been characterised by X-ray crystallography.
TL;DR: Vinyl potassium was formed directly from ethene by use of a new butyl-lithium-potassium t-butoxide-tetramethylethylenediamine metallating reagent; typical products were obtained with 1bromo-octane and, after addition of LiBr in tetrahydrofuran, with benzaldehyde and diphenyl disulphide as mentioned in this paper.
Abstract: Vinyl potassium was formed directly from ethene by use of a new butyl-lithium–potassium t-butoxide–tetramethylethylenediamine metallating reagent; typical products were obtained with 1-bromo-octane and, after addition of LiBr in tetrahydrofuran, with benzaldehyde and diphenyl disulphide.
TL;DR: Treatment with pmdeta in toluene of [Li(thf)4][Li{C(SiMe3)3}2] containing LiCl has given a linear cation in which the chlorine-centred cation is linear as mentioned in this paper.
Abstract: Treatment with pmdeta [pmdeta = Me2N(CH2)2NMe(CH2)2NMe(CH2)2NMe2] in toluene of [Li(thf)4][Li{C(SiMe3)3}2](thf = tetrahydrofuran) containing LiCl has given [(pmdeta)Li(µ-Cl]Li(pmdeta)][Li{C(SiMe3)3}2], in which the chlorine-centred cation is linear.
TL;DR: L'oxydation sur electrode de platine dans le THF de dialkylamidures de lithium ou de bromures de dialklaminomagnesium conduit aux (dialkylamino-2 perhydro) furannes as mentioned in this paper.
Abstract: L'oxydation sur electrode de platine dans le THF de dialkylamidures de lithium ou de bromures de dialkylaminomagnesium conduit aux (dialkylamino-2 perhydro) furannes
TL;DR: In this article, the parity-violating weak interactions were used to stabilize tetrahydrofuran conformations relative to their C3-endomain enantiomers.
TL;DR: In this article, the free energies and enthalpies of water and some hydrocarbons (hexane, cyclohexane), ethers (diethyl ether, tetrahydrofuran) and ketones (propanone, pentan-3-one, cyclopentanone) in octan-1-ol have been determined at 298.15 K from vapour-pressure measurements of dilute solutions and from limiting heats of solution.
Abstract: Free energies and enthalpies of solvation of water and some hydrocarbons (hexane, cyclohexane), ethers (diethyl ether, tetrahydrofuran) and ketones (propanone, pentan-3-one, cyclopentanone) in octan-1-ol have been determined at 298.15 K from vapour-pressure measurements of dilute solutions and from limiting heats of solution. These solvation functions in octanol have been used together with the corresponding hydration functions in order to obtain water–octan-1-ol partition coefficients and their dependence on temperature. A comparison is made with the practical partition coefficients relative to mutually saturated solvents.