Showing papers on "Intramolecular force published in 1984"
TL;DR: Recent advances and examples of the intramolecular Diels-Alder reaction are summarized and applications to the total synthesis of natural products, both completed and in progress, noted as discussed by the authors.
Abstract: Recent advances and examples of the intramolecular Diels–Alder reaction are summarized and applications to the total synthesis of natural products, both completed and in progress, noted. A detailed...
296 citations
TL;DR: In this article, a systematic analysis of K shell excitation spectra of gas phase molecules containing B, C, N, O, and F reveals a correlation between the position of a characteristic K shell feature, the σ shape resonance, and the intramolecular bond length.
Abstract: A systematic analysis of K shell excitation spectra of gas phase molecules containing B, C, N, O, and F reveals a correlation between the position of a characteristic K shell excitation feature, the σ shape resonance, and the intramolecular bond length. When referenced to the 1s ionization threshold the position of the σ shape resonance is found to vary linearly with the internuclear distance between the pair of atoms which gives rise to the scattering resonance. This linear relationship holds remarkably well within different classes of molecules characterized by the total number of electrons (sum of atomic numbers) for a given pair of atoms. The empirically derived rules are compared with the predictions of a full multiple scattering theory treatment. Comparison of empirical experimental and first‐principle theoretical results allows the prediction of the average intramolecular muffin tin potential in the presence of the core hole.
271 citations
TL;DR: In this article, photolysis of several hydroxy compounds in presence of iodosobenzene diacetate and iodine leads to alkoxy radical derivatives which undergo intramolecular hydrogen abstraction to produce cyclic ethers in good yield.
185 citations
TL;DR: In this paper, the one-electron reduction of pentaaminecobalt (III) attached to gold and mercury electrodes via thioalkylcarboxylate ligands containing varying numbers, n, of alkyl carbons was investigated.
Abstract: : Unimolecular electron-transfer rate constants, k sub et, are reported for the one-electron reduction of pentaaminecobalt (III) attached to gold and mercury electrodes via thioalkylcarboxylate ligands containing varying numbers, n, of alkyl carbons. While similar values of k sub et were found at mercury for each reaction, for close-packed monolayers at gold the k sub et values decreased by circa 10 to the 4th power as an increased from one to five. This effect is identified with increasingly nonadiabatic pathways as an increases, a linear plot of log k sub et versus n being obtained. The results provide estimates of the electronic transmission coefficient as a function of the surface-Co(III) separation distance.
170 citations
TL;DR: In this article, a potential surface for deformable water molecules is constructed using an accurate local-mode intramolecular model together with a realistic semi-empirical intermolecular interaction.
162 citations
138 citations
TL;DR: In the presence of AIBN, radicaux α-acylamino peuvent etre generes par traitement de derives de phenylthio-2-, phenylseleno-2 ou methylthios-2 butene-3'yl-1 pyrrolidones-2 par l'hydrure de tributyl-sn in presence of artificial intelligence.
Abstract: Des radicaux α-acylamino peuvent etre generes par traitement de derives de phenylthio-2-, phenylseleno-2 ou methylthio-2 butene-3'yl-1 pyrrolidones-2 par l'hydrure de tributyl-Sn en presence de AIBN. Ces radicaux subissent des reactions intramoleculaires pour donner des indolizidinones et des pyrrolizidinones
134 citations
TL;DR: In this article, an additive procedure (SIBFA) is developed for the rapid computation of conformational energy variations in very large molecules, where the macromolecule is built out of constitutive molecular fragments and the intramolecular energy is computed as a sum of interaction energies between the fragments.
Abstract: An additive procedure (SIBFA) is developed for the rapid computation of conformational energy variations in very large molecules. The macromolecule is built out of constitutive molecular fragments and the intramolecular energy is computed as a sum of interaction energies between the fragments. The electrostatic and the polarization components are calculated using multicenter multipole expansions of theab initio SCF electron density of the fragments. The repulsion component is obtained as a sum of bond and lone pair interactions. Tests of the procedure on a series of model compounds containing ether oxygens and pyridine-like nitrogens are reported and compared with the results of correspondingab initio SCF calculations. The resulting methodology is compatible with the simultaneous computation of intermolecular interactions.
130 citations
126 citations
124 citations
TL;DR: In this paper, new and efficient procedures are described for the conversion of homoallylic alcohols to esters of diazoacetic acid and for the further intramolecular cyclopropanation of those esters.
Book•
01 Mar 1984
TL;DR: In this paper, the Intramolecular Diels-Alder Reaction: Variations and Scope is discussed. But the main focus is on the effect of the Dienophile substitutions on the rate of cyclization.
Abstract: 1. The Intramolecular Diels-Alder Reaction: Variations and Scope.- I. Introduction.- II. Range and Preparation of Dienes.- III. Range and Preparation of Dienophiles.- IV. Heterodienes and Dienophiles.- V. Catalysis of the Reaction.- VI. Conclusion.- VII. References.- 2. The Intramolecular Diels-Alder Reaction: Reactivity and Stereocontrol.- I. Introduction.- II. Factors Influencing the Rate of Cyclization.- 1. Influence of Dienophile Substitution on the Rate of Cyclization.- 2. Influence of Diene Substitution on the Rate of Cyclization.- 3. Influence of the Elements Bridging the Diene and Dienophile on the Rate of Cyclization.- a) Effect of Ring Size.- b) Effect of Buttressing.- c) Effect of Heteroatoms in the Bridge on the Rate of Cyclization.- III. Factors Influencing the Stereochemical Outcome of the Cyclization.- 1. Triene Geometry.- 2. Cis vs. Trans Ring Fusion.- a) Preference for an Endo Transition State.- b) Influence of Diene Substitution on the Geometry of Ring Fusion.- c) Influence of the Bridge Between the Diene and the Dienophile on the Geometry of Ring Fusion.- 3. Diastereomeric Control by Remote Chiral Centers.- a) Diastereomeric Control by a Rigid Skew in the Bridge.- b) Diastereomeric Control by a Substituent on the Bridge.- c) Diastereomeric Control by an Alkoxy Substituent on the Bridge.- d) Diastereomeric Control by Chiral Centers not Included in the Bridge.- IV. Summary.- V. References.- 3. The Intramolecular Alder Ene Reaction.- I. Introduction.- II. Reactivity of Ene Acceptors.- 1. Unactivated Olefins.- 2. Activated Olefins.- 3. Acetylenes.- III. Reactivity of Ene Donors.- 1. Unactivated Donors.- 2. Speculations on Activated Donors.- IV. Steric and Stereoelectronic Control Elements in the Intramolecular Ene Reaction.- 1. Cis vs. Trans Relationship of the Two Interacting Side Chains.- 2. Diastereometric Control by Substituents on the Bridge Between the Ene Donor and the Ene Acceptor.- 3. Diastereomeric Control of Carbon-Carbon Bond Formation by Other Remote Substituents.- V. Directions for the Future.- VI. Tables.- 1. Carbocyclic, Type I, Unactivated Olefin Acceptor.- 2. Carbocyclic, Type I, Activated Olefm Acceptor.- 3. Carbocyclic, Type I, Acetylene Acceptor.- 4. Heterocyclic, Type I, Unactivated Olefin Acceptor.- 5. Heterocyclic, Type I, Activated Olefin Acceptor.- 6. Heterocyclic, Type I, Acetylene Acceptor.- 7. Type II.- 8. Type III.- 9. Organometallic.- VII. References.
01 Dec 1984
TL;DR: In this paper, Monte Carlo simulations are used with models of the intramolecular and intermolecular potential surfaces to model liquid water and several phases of ice, and a quantum local mode analysis of the Monte Carlo configurations is used to predict the density of states and infrared absorption intensities for the bending and stretching vibrations.
Abstract: Monte Carlo simulations are used, together with models of the intramolecular and intermolecular potential surfaces, to model liquid water and several phases of ice. Intramolecular relaxation makes important contributions to both thermodynamic and structural properties. A quantum local mode analysis of the Monte Carlo configurations is used to predict the density of states and infrared absorption intensities for the intramolecular bending and stretching vibrations. The large shifts from the gas phase OH stretch frequencies observed experimentally in the liquid and solid phases are due to anharmonic terms in the intramolecular surface rather than to harmonic intermolecular coupling. A significant contribution to observed changes in IR intensity on condensation arises from the large molecular polarisability.
TL;DR: In this paper, two approaches, one experimental and the other theoretical, to the elucidation of CH bond length variation due to the intramolecular environment are compared, one based on the concept of isolated CH stretching frequencies while the other involves the ab initio gradient procedure.
TL;DR: In this paper, a partir du derive t-butyldimethylsiloxymethyl-4, synthese du tetrahydro-3,6,7,8 benzo [1,2-b: 4,3-b] dipyrroledicarboxylates-2,6
Abstract: Additions intramoleculaires de N-alcyne-3yl chloro-6 pyridazinecarbamates-3 de methyle: obtention d'indolinecarboxylates-1 de methyle; a partir du derive t-butyldimethylsiloxymethyl-4, synthese du tetrahydro-3,6,7,8 benzo [1,2-b: 4,3-b'] dipyrroledicarboxylates-2,6
TL;DR: In this paper, the authors showed that the emitting state of 5,5′-bi-benz[a]-pyrenyl possesses a high dipole moment and a structured twisted intramolecular charge transfer band, which puts an upper limit to the dipolar solvent fluctuations necessary to induce symmetry reduction and charge separation in the excited state.
TL;DR: In this paper, an unstable associate of the 6-cis and 2,6-dicis-2-4 retinals and bacterioopsin is formed, possibly allowed by the lack of the cyclohexyl ring and thus the greater flexibility of the chromophore.
Abstract: samples at 80 K. The C-C band at 1558 cm-' represents the initial all-trans pigment while that at 1575 cm-* almost certainly arises from the short-wavelength M-type intermediate absorbing at ca. 380 nm. The results agree with previously determined correlation between A, and C=C stretching frequency and expected temperature dependence of M formation.12 On combination of the 6-cis and 2,6-dicis isomers of 2-4 with bacterioopsin, a broad absorption is noted with a A, , of 450-460 nm with a shoulder at 510 nm. Extraction of the pigment with methylene chloride yields the respective 6-cis or 2,6-dicis isomer. These pigments are rapidly (5 min) destroyed by hydroxylamine or all-trans-retinal. On irradiation, the absorption shifts to 487 nm, increases in intensity, and is identical with that of the all-trans pigments. Only the respective all-trans isomer is obtained when these irradiated pigments are extracted with methylene chloride. These results indicate that an unstable associate of the 6-cisand 2,6-dicis-2-4 retinals and bacterioopsin is formed, possibly allowed by the lack of the cyclohexyl ring and thus the greater flexibility of the chromophore. The above experiments demonstrate that these acyclic chromophores can form pigments with bacterioopsin which show light-induced absorption and pH changes. As these retinal derivatives lack both a cyclohexyl ring and the fifth C=C, neither of these structural elements are evidently essential for these functions of the pigment. A similar but more restrictive conclusion has been proposed for the 5,6-ethylene bond by our studies of the 5,6-dihydroretinal pigments.13 These results are consistent with isomerization and charge separation being thd primary event14 and indicate that the proton pumping and photocycling are dependent on the polyene chain portion of the retinal chromophore.
TL;DR: In this paper, a single-crystal time-of-flight neutron diffraction structure of hydrogen cis-diacetyltetracarbonylrhenate, (cis-(OH)/sub 4/Re(CH/sub 3/CO)/sub 2/)H, is reported.
Abstract: A single-crystal time-of-flight neutron diffraction structure of hydrogen cis-diacetyltetracarbonylrhenate, (cis-(OH)/sub 4/Re(CH/sub 3/CO)/sub 2/)H, is reported. This is one of the first successful structure determinations reported by using this technique. The diffraction data were collected at the Argonne Intense Pulsed Neutron Source with the unique time-of-flight single-crystal diffractometer. Complete experimental details are provided. The positions of all hydrogen atoms are determined, and the enolic hydrogen atom is shown to participate in an intramolecular O...H...O hydrogen bond. Although large thermal motion of the enolic hydrogen atom prevents a precise definition of the symmetry of this hydrogen bond, most of the results are consistent with an asymmetric O...H...O bond and a localized ..pi..-electron system within the rhena chelate ring.
Journal Article•
TL;DR: In this article, the authors used the neutron powder profile refinement technique to determine the crystal structure of solid Br2 at 5, 80, 170 and 250 K and that of solid Cl2 at 22, 55, 100 and 160 K.
Abstract: The neutron powder profile refinement technique has been used to determine the crystal structure of solid Br2 at 5, 80, 170 and 250 K and that of solid Cl2 at 22, 55, 100 and 160 K. The results confirm that the structures of the two halogens are isomorphous, with space group Cmca at all temperatures. For both halogens the lattice parameters a and b increase monotonically with temperature, but the lattice parameter c decreases at the highest temperatures. The data were analysed assuming both isotropic and anisotropic thermal parameters. The intramolecular bond length and its orientation relative to the b-axis show little change with temperature. For Br2 at 5 K the bond length is 2·301(2) A while a = 6·5672(3), b = 4·4678(2), c = 8·6938(4) A. For Cl2 at 22 K the bond length is 1·994(2) A while a = 6·1453(2), b = 4·3954(1), c = 8·1537(2) A, where the errors quoted are those produced by the profile fitting program.
TL;DR: In this paper, the Dioxabicycloheptan (IIa) in H2O with einer Geschwindigkeit zersetzt, was um 2 Grosenordnungen hoher ist als die von Reaktionen in Losungsmitteln vergleichbarer Polaritat.
Abstract: Im Gegensatz zum Endoperoxid (I) wird das Dioxabicycloheptan (IIa) in H2O mit einer Geschwindigkeit zersetzt, die um 2 Grosenordnungen hoher ist als die von Reaktionen in Losungsmitteln vergleichbarer Polaritat. Fur die Aldehydbildung aus (IIa) und (IIb) ergibt sich ein kinetischer Isotopieeffekt (KIE) von l.5 aber kein D-Verlust und keine pH-Abhangigkeit der Reaktionsgeschwindigkeit.
TL;DR: In this paper, the authors present an overview of cyclohexenes and their application in the context of inter-ramolecular RDA and inter-cellular RDA.
Abstract: I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 11. Thermochemistry and kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 111. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 A. Orbital symmetry considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 B. Stereochemical approach . . . . . . . . . . . . . . . . . . . . . . 97 IV. Scope and limitations . . . . . . . . . . . . . . . . 101 A. Substituted cyclohexenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 B. Norbornene derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 C. Other bridged systems . . . . . . . . . . . . . . . . . . . . . . . . . 114 D. Ortho-condensed systems . . . . . . . . . . 117 E. Intramolecular RDA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 F. Heterocyclic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
TL;DR: In this article, a new resolution method for the analytical and preparative separation of enantiomeric alkanolamines into their antipodes is presented, which involves formation of the monoesters of the alkanolamine with optically pure and symmetrically O,O- disubstituted (R,R )- or (S,S )-tartaric acids.
TL;DR: In this paper, K-shell excitation spectra of gas-phase molecules containing at least two atoms of either B, C. N. O or F revealed the existence of a striking correlation between the bond length of the atomic pair.
TL;DR: In this article, the 2pπ*→3dπ interaction in the excited state of aromatic silanes has been studied by means of absorption and emission spectroscopy, and it has been shown that the c.t. emission originates from the 1(2pπ, 3dπ) state produced by the 2π*(aromatic ring)→ 3Dπ(Si-Si bond) intramolecular charge transfer.
Abstract: The 2pπ*–3dπ interaction in the excited state of aromatic silanes has been studied by means of absorption and emission spectroscopy. Broad and structureless fluorescence spectra of phenyldisilanes and naphthyldisilanes with large Stokes shifts have been observed and they have been attributed to the emissions from the intramolecular charge-transfer (c.t.) states with large dipole moments. Evidence that the c.t. emission originates from the 1(2pπ, 3dπ) state produced by the 2pπ*(aromatic ring)→ 3dπ(Si—Si bond) intramolecular charge transfer is given by the effect of steric twisting on the emission. It is shown that the fast formation (⩽ 1 ns) of the c.t. state from the locally excited state 1(π, π*)1B2(or 1Lb) of phenyldisilanes takes place, followed by rapid decay (⩽ 1 ns) of the intersystem crossing 1(2pπ, 3dπ)→3(π, π*). However, no c.t. emission has been observed for aromatic monosilanes and polycyclic aromatic disilanes (aromatic rings 3) even in fluid polar solvents. The 2pπ*→3dπ intramolecular c.t. mechanism is discussed in comparison with that of the twisted intramolecular charge-transfer (t.i.c.t.) state.
TL;DR: In this paper, the authors determined des structures cristallines des trois composes and showed that the distorsion structurale is due a une tendance a une geometrie bipyramidale trigonale.
Abstract: Determination des structures cristallines des trois composes. La distorsion structurale est due a une tendance a une geometrie bipyramidale trigonale. Spectres IR et RMN montrant que les structures sont retenues en solution. Discussion sur les systemes de liaison hydrogene