Showing papers on "Intramolecular force published in 1989"
TL;DR: In this paper, the available space for incoming reagents by a variation of the alkyl substituents at the nitrogen donor atoms was modeled, and the first experiments aimed at modelling the available spaces for incoming Reagents were described, which lead to "trapped intermediates" with a considerable stability.
Abstract: Research on the chemistry of monoanionic aryl ligands having ortho- or bis-orthodimethylaminomethyl substituents, i.e., C6H4(CHzNMe2)-2, A, CioHgNMe2-8, B and cgH3(CH2NMe2)2-2,6, C, that form organometallic compounds with a direct M-Ca 1 o-bond, WIII be discussed. Through coordination of the N-donor site(s) of the ortho CH2NMe2 arm(s) five-meaered M-C-C-C-N chelate ring formation occurs. In particular, the rigid bis-ortho chelation of the terdentate ligand C provides the complexed metal centre with a set of unusual properties. Firstly, this ligand restricts the number of coordination sites that are available for incoming reagents and other li ands This is a situation that can frustrate the normal course of, for example, an oxidative reaction at the N donor atoms make these ligands extremely electron-rich and consequently they afford coniplexed (d8) metal centres with an enhanced nucleophilicity. Together, these features provide their complexes with unexpected and novel properties; e.g. q I-coordination of 12 to PtlI, stable NiI'I-carbon bonds, and intramolecular rearrangements involving C-H bond activation. Here, the first experiments aimed at modelling the available space for incoming reagents by a variation of the alkyl substituents at the nitrogen donor atoms will be described. bound d 53' metal centre and lead to "trapped intermediates" with a considerable stability. Secondly, the hard C and
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213 citations
TL;DR: In this paper, the deformation of the benzene skeleton plays an important role in the dynamic process of intramolecular proton transfer in the first excited 1π, π*) state of o-hydroxybenzaldehyde.
153 citations
TL;DR: A method has been developed, based on global analysis of both donor and acceptor fluorescence decay curves, which overcomes this extreme cross-correlation and allows the parameters of the equilibrium distance distributions and intramolecular diffusion constants to be recovered with high statistical significance and accuracy.
149 citations
TL;DR: In this article, an experimental study of the distance dependence of intramolecular, long-distance hole transfer in organic radical cations has been performed, where the aromatic donor and acceptor groups, biphenyl and naphthalene (D and A), were held at fixed distances by five rigid saturated hydrocarbon spacer groups.
Abstract: An experimental study of the distance dependence of intramolecular, long-distance hole transfer in organic radical cations has been performed. The aromatic donor and acceptor groups, biphenyl and naphthalene (D and A), were held at fixed distances by five rigid saturated hydrocarbon spacer groups. The kinetics of the transfer reactions (D{sup +}SA {yields} DSA{sup +}) were monitored by transient absorption of the hole donor, 4-biphenylyl radical cation. Intramolecular hole-transfer rate constants were determined for this process and compared with previous results for electron transfer in radical anions of the identical molecules. A comparison of the hole- and electron-transfer results reveals that the attenuation of the rate constants, and therefore the electronic coupling, as a function of distance is the same for both within the limits of error of the experiment.
144 citations
TL;DR: In this article, the formation and decomposition of negative molecular ions following low energy electron capture is studied using electron attachment and electron transmission spectroscopy, and an analysis of the kinetic energy release of the reaction products is performed in order to obtain information on the intramolecular decomposition dynamics of the transient negative parent ions.
130 citations
121 citations
TL;DR: A new synthesis of imidazolinones and quinazolinone by intramolecular aza-Wittig reaction was described in this paper, where the Staudinger reaction was used.
121 citations
TL;DR: In this article, the effect of conformation changes on the free energy barrier to intramolecular electron transfer is examined for systems containing two redox centers and the relative energies of the conformers determine whether the observed electron-transfer reaction proceeds by a two-step mechanism involving the intermediate formation of an unstable conformer or by a direct (concerted) reaction involving only the stable reactant and product.
Abstract: The interaction between conformation changes and electron-transfer rates is considered for systems containing two redox centers. The effect of conformation changes on the free-energy barrier to intramolecular electron transfer is examined. Unstable conformers R* of the reactant (or P* of the product) that are either more (low-{lambda} intermediates) or less (high-{lambda} intermediates) redox-active than the stable reactant R (or product P) are considered. The relative energies of the conformers determine whether the observed electron-transfer reaction proceeds by a two-step mechanism involving the intermediate formation of an unstable conformer or by a direct (concerted) reaction involving only the stable reactant and product. The present analysis generates a set of equations that indicate when the two-step or the direct mechanism is energetically favored. Only when the two-step mechanisms are favored is gating or conformational control possible.
115 citations
TL;DR: The solvent-induced interactions between two kinds of molecules (or groups) are examined from the point of view of the solvation free energies of a pair of interacting molecules as discussed by the authors, and it is argued that intramolecular hydrophilic interactions are probably more significant in biochemical processes than hydrophobic interactions.
Abstract: The solvent‐induced interactions between two kinds of molecules (or groups) are examined from the point of view of the solvation free energies of a pair of interacting molecules (or groups) The first interaction is that between two simple nonpolar solutes (or groups) in water and is known as the hydrophobic interaction Both theoretical as well as experimental evidence indicate that these interactions are quite weak The solvent‐induced interactions between two functional groups that can form hydrogen bonds, referred to as intramolecular hydrophilic interactions, are found to be much stronger than the corresponding hydrophobic interactions It is therefore argued that intramolecular hydrophilic interactions are probably more significant in biochemical processes than hydrophobic interactions
TL;DR: The combination of (dba) 3 Pd 2 ·CHCl 3 plus a car-ylic acid effectively catalyzes cyclization of 1,6-enynes in which asymmetric induction may be achieved by use of enantiomerically pure car-sylic acids as mentioned in this paper.
TL;DR: In this paper, the transfert d'electron intramoleculaire de dimethylamino-4'' benzyl-4' benzyl 9-and benzyl nine anthracenes is described.
Abstract: Etude du transfert d'electron intramoleculaire de dimethylamino-4'' benzyl-4' benzyl-9- et benzyl-9 anthracenes
TL;DR: Starting from 5-hydroxy-1-pentenes, palladium-catalyzed intramolecular alkoxy carbonylation produces 2,5-disubstituted tetrahydrofurans in good yield.
Abstract: Starting from 5-hydroxy-1-pentenes, palladium-catalyzed intramolecular alkoxycarbonylation produces 2,5-disubstituted tetrahydrofurans in good yield
TL;DR: In this article, a molecular model for glycerol was constructed and applied to a study of clusters and condensed phases by molecular dynamics simulation, each molecule was regarded as a flexible polar complex of nine mass points (CH and CH2 groups are treated as ‘‘united atoms’’).
Abstract: A molecular model has been constructed for glycerol and has been applied to a study of clusters and condensed phases by molecular dynamics simulation. Each molecule is regarded as a flexible polar complex of nine mass points (CH and CH2 groups are treated as ‘‘united atoms’’). Periodic arrays stabilize in a close approximation to the observed glycerol crystal structure, with identical extended molecules connected by infinite chains of hydrogen bonds. By contrast the stable and supercooled liquids display a variety of asymmetrical molecular conformations and an irregular network of hydrogen bonds. Detailed examination of the various atomic pair correlation functions reveals considerable overlap of intramolecular and intermolecular features, implying intrinsic ambiguity in the interpretation of x‐ray and neutron diffraction measurements designed to determine the short‐range order of liquid glycerol.
TL;DR: In this article, a detailed structural analysis of the series of donor-acceptor molecules O2NC6H4(C~C),C6H 4NH2 (n = 0-3) has been performed in order to investigate ground-state donor acceptor interactions through a conjugated framework.
Abstract: A detailed structural analysis of the series of donor-acceptor molecules O2NC6H4(C~C),C6H4NH2 (n = 0-3) has been performed in order to investigate ground-state donor-acceptor interactions through a conjugated framework. The results of the investigation reveal an unusual bonding pattern that is not adequately explained by a simple quinonoid resonance structure resulting from bond migration through the conjugated backbone. Instead, the charge-transfer character manifests itself through quinonoid distortions only of the nitrophenyl and aminophenyl functional groups themselves. Evidence is presented that indicates an intramolecular origin for the charge transfer. The acetylene bridges, which must participate in the migration of charge, are not themselves structurally altered. These observations lead to the conclusion that the charge-transfer character in the ground state is not highly delocalized but results in charges localized in the acceptor orbitals. Weak powder second harmonic generation was observed from the compounds with n = 1-3. This is discussed relative to the single-crystal X-ray structures.
TL;DR: In this paper, selective desilylation was used to generate α-amineradicals from α-alkyl silylamine radical cation and their intramolecular cyclisation.
TL;DR: The intramolecular nitrile oxide cycloaddition (INOC) of a series of unsaturated oximino ethers has been investigated in this article, where the preferred stereoisomer in the formation of the five-and six-membered ring ethers is trans, whereas in the sixmembered round ethers the cis isomer predominates.
Abstract: The intramolecular nitrile oxide cycloaddition (INOC) of a series of unsaturated oximino ethers has been investigated. The synthesis of the olefinic nitrile oxides involves treating an unsaturated alcohol with a {alpha}-bromoalkanal O-(trimethylsilyl)oxime in the presence of fluoride ion followed by subsequent sodium hypochlorite oxidation. The nitrile oxides were not isolated but spontaneously underwent intramolecular cycloaddition to give fused five- and six-membered ring ethers. The preferred stereoisomer in the formation of the five-membered ring ethers is trans, whereas in the six-membered ring ethers the cis isomer predominates. MM2 calculations help rationalize the observed stereoselectivity. The ratio of diastereomeric products from the INOC reaction appears to correlate with product stabilities. Simple heating of some of the oximino ethers led to intramolecular cycloaddition. The ring closure apparently proceeds subsequent to a tautomeric equilibration of the oxime with a transient nitrone which is trapped by the neighboring {pi}-bond.
TL;DR: The photolyses of 5α-cholestane-3β,6β-diol 3-acetate (1), 5α cholestan-2β-ol (4), 5β-choline-4β-OL (8), (20R)-pregn-5-ene-3 β,20-dioxioxioxyl-20diol (3-β,20dioxyl)-3-acetates (19), and dihydrotigogenin-3acetate(25) in the presence of
Abstract: The photolyses of 5α-cholestane-3β,6β-diol 3-acetate (1), 5α-cholestan-2β-ol (4), 5α-cholestan-4β-ol (8), (20R)-pregn-5-ene-3β,20-diol 3-acetate (19), (20S)-pregn-5-ene-3β,20-diol 3-acetate (21), and dihydrotigogenin 3-acetate (25) in the presence of iodine and various hypervalent organoiodine compounds lead to alkoxyl radicals which undergo intramolecular hydrogen abstraction to produce, in most cases, 1,4-iodohydrins and tetrahydrofuran derivatives.
TL;DR: The infrared spectrum of the ammonia water complex has been recorded from 10 to 4000 cm−1 for complexes trapped in neon and krypton matrices as discussed by the authors, and the observed intramolecular fundamentals are compared with frequencies calculated from a rigid-molecule harmonic oscillator model.
Abstract: The infrared spectrum of the ammonia water complex has been recorded from 10 to 4000 cm−1 for complexes trapped in neon and krypton matrices. Spectra have been observed for NH3 or ND3 complexed with H2O, HDO, or D2O. The observed intramolecular fundamentals are compared with frequencies calculated from a rigid‐molecule harmonic oscillator model.
TL;DR: In this article, the authors compared the Cg, Q, and Cg structures with the C$ and CT structures and showed that the CT hydrogen bond is the strongest, in agreement with the NH.