Showing papers on "Intramolecular force published in 1992"
Book•
01 Jun 1992
TL;DR: In this article, the authors present a survey of conjugate receptors and their interaction with the nucleophiles, as well as a classification of reaction types and their relations with each other.
Abstract: Introduction. Organization of the book. History. Nomenclature, classification of reaction types and survey of conjugate receptors. Mechanism of conjugate additions. The nucleophiles. Intramolecular reactions. Tandem reactions. Alkenals and Acyclic Alkenones. Introduction. Intermolecular reactions. Intramolecular reactions. Cycloalkenones. Introduction. Intermolecular reactions. Intramolecular reactions. Alkenoic Acids and their Derivatives. Introduction. Intermolecular reactions. Intramolecular reactions. alpha,beta-Unsaturated Lactones and Lactams. Introduction. Stabilized carbanions. Organocopper reagents. Other organometallic reagents. Free radicals. Heteronucleophiles. Other Systems. Introduction. Nitroalkenes. Alkenylsulfoxides, phosphonates and related compounds. Quinones. Alkenylsilanes. Ketene acetals. Alkenylphosphonium salts. Activated Alkynes. Alkynones. Alkynoic acid derivatives. Alkynyl sulfoxides, and related sustems. Index.
741 citations
TL;DR: A review of dihydrogen-dihydride reactions can be found in this article, where the authors present a line-shape analysis of a three-hydrogen system M(H,)H.
630 citations
TL;DR: Palladium-catalysed reactions involving organotin compounds are of rapidly increasing importance in organic synthesis as mentioned in this paper, and a variety of applications in natural product synthesis have been described, and intramolecular reactions can be used for the formation of small, medium and large rings.
Abstract: Palladium-catalysed reactions involving organotin compounds are of rapidly increasing importance in organic synthesis. Carbon-carbon bond formation via cross-coupling reactions is of primary interest in view of the variety of functionalities which can be used. A variety of applications in natural product synthesis have been described, and intramolecular reactions can be used for the formation of small, medium and large rings. Reactions involving additions of tin-element bonds to multiply bonded systems are also of increasing significance. Although «general-purpose» catalysts are available, specific catalysts are often required for certain applications
351 citations
309 citations
TL;DR: The role of the secondary structure of polyproline II in facilitating long-range electron transfer was explored in this article, where the role of peptide and protein in mediating electron transfer is discussed.
Abstract: Electron transfer is one of the fundamental reactions in biological photosynthesis, respiration, and redox-mediated enzyme catalysis. Understanding the role of peptides and proteins in mediating long-range electron transfer has important physical, chemical, and biological implications. Intramolecular electron-transfer reactions, where electron transfer occurs between donor and acceptor sites separated by a synthetic peptide or protein fragment, have so far provided the most insight into the role of the peptide and protein in mediating electron transfer. This article reviews the work the authors' group and others on small molecule systems that have been designed and studied to explore long-range electron-transfer pathways available between a donor and an acceptor separated by a rigid peptide framework. The role of the secondary structure of polyproline II in facilitating these mediations is explored. 87 refs., 3 figs, 5 tabs.
253 citations
TL;DR: The theory of atoms in molecules demonstrates the existence of an intramolecular hydrogen bond between a methyl group and a negatively charged oxygen in the biomolecules creatine and its competitive inhibitor carbamoyl sarcosine as discussed by the authors.
200 citations
198 citations
01 Jun 1992
TL;DR: In this paper, the authors examined intramolecular proton transfer in 2-(2′-hydroxyphenyl)benzoxazole in its electronic S 1 state.
Abstract: We examine intramolecular proton transfer in 2-(2′-hydroxyphenyl)benzoxazole in its electronic S 1 state. The experimental methods are fluorescence spectroscopy of the compound isolated in an argon matrix at 11 K and in a supersonically cooled jet, as well as femtosecond pump-and-probe spectroscopy in cyclohexane at 298 K. From the spectroscopic measurements we conclude that the vibronic bands near the electronic origin have a homogeneous width ⩾ 150 cm −1 , corresponding to a vibronic lifetime of less than 35 fs. Residual structure reveals a short progression in a vibrational mode of 147 cm −1 . The time-resolved measurements indicate a short-lived initial Franck-Condon distribution which evolves, with a time constant of 60±30 fs, into a distribution of vibrational levels which partly belong to the excited keto form of the molecule. The molecular geometries of the excited enol and keto forms are calculated using MNDO methods. For these geometries, the positions of the mobile hydrogen atom are separated by 0.41 A. We construct a model potential for excited-state intramolecular proton transfer which is consistent with the observations.
192 citations
TL;DR: In this paper, the authors showed that the photoexcitation of a Ru(II) polypyridine complex covalently attached by a flexible link to pyrene results in a rapid intramolecular transfer of triplet energy with a forward rate constant of (1.3 {+-} 0.3) x 10{sup 8} s{sup -1} in deaerated methanol solution.
Abstract: The localized photoexcitation of a Ru(II) polypyridine complex covalently attached by a flexible link to pyrene results in a rapid intramolecular transfer of triplet energy with a forward rate constant of (1.3 {+-} 0.3) x 10{sup 8} s{sup -1} in deaerated methanol solution. On account of the energetic proximity of the states, reverse transfer occurs with a rate constant lower by a factor of 18{+-} 3. This equilibiration is rapid compared with the relaxation processes that are deactivating the system, which have a common lifetime of 11.2 {+-}4 {mu}s. These results may be the first direct observation of an equilibrium being reached in an intramolecular triplet energy transfer reaction. 17 refs., 4 fig.
190 citations
TL;DR: In this article, a full study of the use of phenyl selenoesters as precursors to acyl radicals and their subsequent participation in intermolecular and intramolecular alkene addition reactions is detailed.
Abstract: A full study of the use of phenyl selenoesters as precursors to acyl radicals and their subsequent participation in intermolecular and intramolecular alkene addition reactions is detailed. Primary alkyl-, vinyl-, and aryl- substituted acyl radicals generated by Bu 3 SnH treatment of the corresponding phenyl selenoesters participate cleanly un intermolecular addition reactions with alkenes bearing electron-withdrawing or radical-stabilizing substituents at rates that exceed those of the potentially competitive decarbonylation or reduction
171 citations
TL;DR: In this paper, a reaction pathway involving insertion of the alkyne into the metal- carbon bond of the starting material followed by intramolecular addition of the Y atom to the resulting metallated-vinyl unit is proposed based on both the regioselectivity of the insertion and the existence of genuine isolated intermediates for the formation of the heterocyclic compounds.
Abstract: Cyclometallated compounds obtained via the well-known intramolecular C-H activation by transition metals of N- or S- containing ligands may lead to organic heterocycles through reaction with alkynes. The mechanistic implications of the formation of both C-C and C-Y bonds are discussed. A reaction pathway involving insertion of the alkyne into the metal- carbon bond of the starting material followed by intramolecular addition of the Y atom to the resulting metallated-vinyl unit is proposed based on both the regioselectivity of the insertion and the existence of genuine isolated intermediates for the formation of the heterocyclic compounds.
TL;DR: Samarium (II) iodide in the presence of HMPA effectively promotes the intramolecular coupling of unactivated olefinic ketones by a reductive ketyl-olefin radical-cyclization process as discussed by the authors.
Abstract: Samarium (II) iodide in the presence of HMPA effectively promotes the intramolecular coupling of unactivated olefinic ketones by a reductive ketyl-olefin radical-cyclization process. The reaction is quite for the formation of 5- and 6-membered carbocycles and even provides modest yields in less facile cyclization processes as evidenced by the generation of methylcyclooctanol via an 8-endo cyclization. Sequential radical cyclization-intermolecular nucleophilic addition/substitution process set the SmI 2 reaction apart from its radical-chain,photochemical, and electrochemical counterparts
TL;DR: In this paper, the thermal degradation of commercial perfluoropolyethers (Fomblin Z and Y, Krytox, and Demnum) and PFPEO (perfluoropoly(ethylene oxide)) in the presence of Lewis acids (metal oxides and halides) was examined.
Abstract: Thermal degradation of commercial perfluoropolyethers (Fomblin Z and Y, Krytox, and Demnum) and PFPEO (perfluoropoly(ethylene oxide)) in the presence of Lewis acids (metal oxides and halides) was examined. It is shown that the degradation is dominated by the intramolecular disproportionation process of the following scheme RCF 2 OCF 2 (CH 2 ) 3 OR → RCOF + CF 3 (CH 2 ) 3 OR. The reaction occurs when the two oxygen atoms flanking a monomer unit of polyether chains interact with a Lewis acid site(s). The differentail charges induced at the carbons immediately outside and inside the unit cause a fluorine transdfer and effect the disproportionation process
TL;DR: An 800 ps molecular dynamics simulation of antamanide in chloroform has been used to study the influence of fast angular and radial intramolecular dynamics on experimentally accessible homonuclear NMR cross-relaxation rates.
Abstract: An 800 ps molecular dynamics simulation of antamanide in chloroform has been used to study the influence of fast angular and radial intramolecular dynamics on experimentally accessible homonuclear NMR cross-relaxation rates. Correlation functions of the intramolecular motions, needed to compute the cross-relaxation rate constants, are derived from the molecular dynamics simulation. The spatial restriction of the relative motion of two nuclei involved in the cross relaxation is described by an angular and a radial order parameter in a molecule-fixed reference frame
TL;DR: In this article, an attempt was made to explain the dissolving behavior of natural celluloses in aq. alkali solution in terms of super-molecular structure and the degree of break-down of O3-H···O5′ intramolecular hydrogen bond χam(C3) as previously demonstrated for regenerated celluloses.
Abstract: An attempt was made to explain the dissolving behavior of natural celluloses in aq. alkali solution in terms of super-molecular structure. Cellulose samples with crystal form of cellulose I having the viscosity-average molecular weight of ca. 8×104 and having various solubilities were prepared by applying the methods of so-called steam-explosion treatment and acid-hydrolysis to soft wood pulp and cotton linter. Their solubility towards aq. NaOH solution proved to be governed by the degree of break-down of O3—H···O5′ intramolecular hydrogen bond χam(C3) as previously demonstrated for regenerated celluloses. χam(C6) expressing in part the degree of break-down of O2—H···O6′ intramolecular hydrogen bond was shown to be also closely correlated with the solubility of the cellulose. In addition to χam(C3) and χam(C6), several other super-molecular structural parameters estimated from the infrared spectra of the natural cellulose samples were found to be correlated with solubility and those parameters might represent wide variation of conformation caused by the break-down of intramolecular hydrogen bonds.
TL;DR: Results demonstrate that both Sr2+ and K+ facilitate the intermolecular G-tetraplex formation, with the divalent cation being much more effective.
Abstract: Electrophoretic and spectroscopic studies were made with the telomere-related sequences d(G4T2G4T2G4T2G4) (T2) and d(G4T4G4T4G4T4G4) (T4) in the presence of Na+, K+, and Sr2+. Electrophoretic evidence indicates that these two oligomers exist in multiconformational states in solutions. A band identified as that of intermolecular (tetramolecular) G-quadruplex is apparent in both T2 and T4, whereas a band identified as intramolecular (monomeric) G-quartet is only evident in T4. The remaining electrophoretic bands that exhibit mobilities intermediate of these two extremes are identified as those of hairpin-related duplexes and tetraplexes. In the presence of millimolar concentrations of Sr2+ and subsequent thermal treatment, the intensity corresponding to the band attributable to the intermolecular G-quadruplex is dramatically enhanced in T2 while those of the hairpin-related bands of intermediate mobility are greatly reduced. Similar but less dramatic enhancement of the intermolecular quadruplex band is also observed in T4. Although these effects can also be induced by K+, orders of magnitude higher concentrations are needed. The intensity of the intramolecular G-quartet band, apparent in T4 but not in T2, appears to be relatively insensitive to the type of cation present in the solution. These results demonstrate that both Sr2+ and K+ facilitate the intermolecular G-tetraplex formation, with the divalent cation being much more effective. Comparison with the corresponding CD spectral characteristics suggests that the electrophoretic intensity enhancement of the intermolecular G-quadruplex band is correlated to the intensity enhancement of of the positive CD maximum at 265 nm.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this paper, the excited-state intramolecular proton transfer (ESIPT) for 10-hydroxybenzo[h]quinoline was reported with a maximum at 609 nm and a yield of ≈ 2.0 × 10 −2 in methylcyclohexane at room temperature.
TL;DR: In this paper, the electronic spectra of the amino acids tyrosine and phenylalanine have been measured in a supersonic jet using laser-induced fluorescence spectroscopy.
TL;DR: A new fluorescent calix[4]arene 2 has been synthesized as an intramolecular excimer-forming Na+ sensor which shows a change in fluorescent characteristics specifically upon complexation with Na+ as mentioned in this paper.
Abstract: A new fluorescent calix[4]arene 2 has been synthesized as an intramolecular excimer-forming Na+ sensor which shows a change in fluorescent characteristics specifically upon complexation with Na+
TL;DR: In this paper, a simulation of a 1.791 molal aqueous NaCl solution is performed using a flexible/polarizable five-site water model and the effect of ionic perturbations on properties such as the water intramolecular structure and vibrations, and the solution phase dielectric constant.
Abstract: A classical molecular‐dynamics simulation of a 1.791 molal aqueous NaCl solution is performed using a flexible/polarizable five‐site water model. Through an investigation of the ion‐water pair‐correlation functions and the relative orientation of the waters of hydration, we are able to study the solvation structure in this moderately concentrated salt solution. Under perturbations from the solvated ions, there appears a considerable reorganization of the water molecules. Some of the original intermolecular hydrogen bonding structure is broken down, as bonding with the neighboring cations and anions takes place. Also considered in this paper are the energetics of hydration, and the effect of ionic perturbations on properties such as the water intramolecular structure and vibrations, and the solution phase dielectric constant. An important conclusion from this work is that, in the NaCl solution studied here, perturbations on the water structure by the ions affect mainly intermolecular orientational properties. Although they may be large, these orientational effects are not sensitively detected by many experimental techniques, such as x‐ray diffraction or vibrational spectroscopy.
TL;DR: In this article, a review of the information on both intramolecular forces and inter-molecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexes during the past several years is presented.
Abstract: Measurements of the low-frequency van der Waals vibrations in weakly bound complexes by high-resolution laser spectroscopy provide a means to probe intermolecular forces at unprecedented levels of detail and precision. Several new methods are presently being used to record vibration/rotation-tunneling (VRT) transitions associated with the motions of the weak bonds in van der Waals clusters. The most direct measurements are those probing only the van der Waals modes themselves, which occur at far-infrared wavelengths. This article presents a review of the information on both intramolecular forces and intramolecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexes during the past several years. Some rotationally resolved measurements of van der Waals modes observed in combination with electronic or vibrational excitation are also discussed. 185 refs., 15 figs., 1 tab.
TL;DR: Native-like structure in the intermediates probably causes steric inhibition of direct sequential formation of the three disulfides found in the native protein, thus accounting for the role of intramolecular rearrangements in the folding mechanism of this small protein.
TL;DR: In this article, temperature coefficients of the chemical shifts, scalar coupling constants, and exchange rates for the hydroxyl protons in sucrose in mixtures of water and acetone were measured.
Abstract: We have measured temperature coefficients of the chemical shifts, scalar coupling constants, and exchange rates for the hydroxyl protons in sucrose in mixtures of water and acetone. The values measured are virtually the same for all the hydroxyl protons in sucrose. These observations indicate that there are no persistent hydrogen bonds in sucrose in aqueous solution
TL;DR: Rhodium(I) chiral diphosphine complexes efficiently and rapidly catalyze the intramolecular hydrosilation of silyl ethers derived from allylic alcohols.
Abstract: Rhodium(I) chiral diphosphine complexes efficiently and rapidly catalyze the intramolecular hydrosilation of silyl ethers derived from allylic alcohols. The efficiency and rates of intramolecular hydrosilations were determined for a variety of silyl and olefin substituents. The catalysts were found to tolerate a widevariety of silyl substituents, although terminal alkyl olefin substituents were found to retard catalysis. Terminal aryl olefinsubstituents were found to be hydrosilated efficiently and at reasonable rates
TL;DR: The disulfide bridge linking cysteines-3 and -26 in the blue copper aruzin isolated from Alcaligenes faecalis (Alc.faec) and Pseudomonas fluorescens B (Ps.fluor) reacts with pulse radiolytically produced CO 2 - radical anions to yield the Disulfide radical ion, RSSR -.
Abstract: The disulfide bridge linking cysteines-3 and -26 in the blue copper aruzin isolated from Alcaligenes faecalis (Alc.faec.) and Pseudomonas fluorescens B (Ps.fluor) reacts with pulse radiolytically produced CO 2 - radical anions to yield the disulfide radical ion, RSSR - . This radical then dacays by an intramolecular electron transfer (et) to the Cu(II) center whith is at a distance of ∼2.6nm. At 25 o C and pH 7.0, the rate constants of the intramolecular electron transfer reactions are 11 ± 2 and 22 ± 3 s -1 in Alc. faec. and Ps. Fluor. azurin, respectively
TL;DR: In this paper, the existence of an HO-3⋯O-5′ intramolecular hydrogen bond in methyl β-cellobioside in solution in Me 2 SO-d 6 and H 2 O-CD 3 OD (4:1 w/w) was studied by 500-MHz 1 H-NMR spectroscopy and MD simulations.
TL;DR: Aldoximes and ketoximes possessing γ- or δ-alkenyl substituents undergo thermal conversion to cyclic nitrones via a 1,3-azaprotio cyclotransfer, a 2n + 2σ + 2π concerted process, rather than a Michael addition as mentioned in this paper.