bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Deuterium Quadrupole Coupling Constants in the Liquid Crystalline Phase — Values for Chloroform and Dichloromethane
Authors: Voigt J. , Bjorholm T. , Jacobsen J. P. 
Published: November 2013

AbstractThe deuterium quadrupole coupling constants of chloroform and methylenechloride have been determined as 174.7 ± 0.5 kHz and 167.8 ± 1.3 kHz, respectively. The values were determined from the quadrupole splitting and the 13C, 2H dipole–dipole couplings obtained from the natural abundance 13C‐satellites in the 2H‐NMR spectrum of the molecules in nematic phase. The dipole‐dipole coupling has been corrected for vibrational motion.
Nitrogen‐14 NMR of Solutes in Liquid Crystals: NH4NO3 and (CH3)4N NO3 in the DSCG–Water System
Authors: Gilboa Haggai , Loewenstein Aharon 
Published: November 2013

AbstractMeasurements of the nitrogen‐14 and deuterium quadrupolar splittings in NH4NO3 and (CH3)4 N NO3 dissolved in the disodiumcromoglycate–water liquid crystalline system are presented. Nitrogen‐14 T1 values in aqueous solutions for these salts are also given. The results are discussed and compared with similar studies on solutes containing 14N in ordered media.
Modern Spin Relaxation Techniques for Liquid Crystals: Nuclear Spin Probes in Thermotropic Mesophases
Authors: Vold Robert L. , Vold Regitze R. 
Published: November 2013

AbstractThe existence of well‐resolved dipolar and/or quadrupolar splittings in the NMR spectra of solutes in ordered phases greatly facilitates analysis of nulcear spin relaxation pathways in terms of individual spectral density parameters evaluated at well‐defined frequencies. Both auto‐ and cross‐correlation terms are experimentally accessible via an appropriate combination of modern pulse techniques, and this detailed information is of use in assessing the validity of various models for molecular motion in ordered systems. Spectral density data for small, rigid solutes in nematic mesophases can be rationalized in terms of rotational diffusion, including effects of static order, together with order director fluctuations. The techniques developed for the simpler nematics can readily be used for solutes in the smectic phase as well as for studies of the liquid crystalline solvent molecules themselves.
NMR Relaxation in Thermotropic Liquid Crystals
Authors: Dong Ronald Y. 
Published: November 2013

AbstractIn this review some essential features of the spin relaxation theory in liquid crystals are outlined, with particular emphasis on orientational order director fluctuations and molecular reorientations in anisotropic environments. Experimental relaxation studies using 1H, 2H and 13C nuclei during the past five years are surveyed and compared with existing theories. While the molecular dynamics are relatively well understood in the nematic and smectic phases, more work is needed to further understand cholesteric and discotic mesogens.
Substituent, Temperature, and Solvent Effects in the Singlet Oxygenation of 7‐Alkyl‐ and 7‐Aryl‐substituted 1,3,5‐Cycloheptatrienes
Authors: Adam Waldemar , Rebollo Hector 
Published: November 2013

AbstractSinglet oxygen is a sufficiently reactive dienophile to intervene in the tropilidene‐norcaradiene valence isomerization equilibria of 7‐aryl‐ and 7‐alkyl‐1,3,5‐cycloheptatrienes, leading to both the norcaradiene and tropilidene endoperoxides 2N and 2T, respectively, besides the thermally rather labile 1,2‐dioxetanes 3 and the substituted benzaldehydes 4, derived from the latter on thermal decomposition. Quantitative product studies by 1H‐NMR reveal that the proportion of 2N and 2T endoperoxides is a delicate function of (a) the electronic nature of the 7‐aryl substituent, i.e. the 2N/2T ratio increases in the order p‐Cl > H > p‐OMe, (b) the steric demand of the 7‐alkyl substituent, i.e. the 2N/2T ratio increases in the order tBu > iPr > Et > Me, (c) the temperature of singlet oxygenation, i.e. the 2N/2T ratio increases with increasing temperature, and (d) the polarity of the solvent, i.e. the 2N/2T ratio decreases in the order CCl4 > C6H6 > CH2Cl2 > CH3CN. A mechanism is proposed in which substituent and temperature effects are interpreted in terms of appropriate shifts in the 2T ⇌ 2N equilibria. The solvent effect is rationalized in terms of reversible exciplex formation between the tropilidene isomer and singlet oxygen (electronically excited), leading to the 1,4‐dipolar intermediate 7.
Heterolytic and Homolytic Oxygen Transfer Reactions from d0 Metal Peroxides to Hydrocarbons
Authors: Mimoun Hubert 
Published: November 2013

AbstractAn attempt is made to correlate the catalytic activity of d0 metal complexes in the oxidation of hydrocarbons by H2O2 and ROOH with the oxidizing properties of their peroxidic derivatives. The triangular structure of bound peroxo and alkylperoxidic groups is a common characteristic of d0 metal peroxides. The heterolytic or homolytic nature of the catalytic oxidation is governed by the heterolytic or homolytic cleavage of the triangular peroxidic moiety. The mechanism of selective heterolytic epoxidation involves the peroxymetalation of the coordinated olefin. Homolytic oxidations are less selective and involve the non‐stereospecific epoxidation of olefins and the hydroxylation of alkanes and arenes by biradical peroxidic species.
Radiolytic Studies of the Cumyloxyl Radical in Aqueous Solutions
Authors: Neta P. , Dizdaroglu Miral , Simic Michael G. 
Published: November 2013

AbstractFormation and reactions of the cumyloxyl radical in aqueous solutions were studied by steady‐state and pulse radiolytic techniques. Cumene hydroperoxide reacts with e−aq (k = 4.4 × 109 M−1s−1) to yield the cumyloxyl radical. The spectrum recorded after the pulse indicates formation of a species absorbing at 250 nm. This product was identified as acetophenone, which is formed by the fragmentation of the cumyloxyl radical. By comparison of the pseudo‐first‐order rates of e−aq decay at 600 nm with the rate of production of acetophenone at 245 nm at increasing concentrations of cumene hydroperoxide, it was possible to derive a rate constant of 1.0 × 107 s−1 for the cleavage of cumyloxyl to acetophenone and methyl radical. This value is higher than that measured previously in organic solvents (1 × 106 s−1), as expected. HPLC analysis of the radiation products acetophenone and cumyl alcohol permitted determination of rate constants for hydrogen abstraction by the cumyloxyl radical, in competition with the fragmentation. The rate constants for H abstraction from i‐PrOH, EtOH, and MeOH by CmO were found to be 9.9 × 106, 3.8 × 106, and 8.5 × 105 M−1 s−1, respectively.
Measurement of Absolute Propagation and Termination Rate Constants for Alkylperoxyls in Solution by the Hydroperoxide Method
Authors: Howard J. A. 
Published: November 2013

AbstractKinetic and product studies of liquid phase autoxidations in the presence of high concentrations of alkyl hydroperoxides have enabled absolute propagation and termination rate constants for alkylperoxyls to be measured. A large number of rate constants and activation parameters have been accumulated over the past few years by this technique and the highlights of this work are presented in this review.
Organoboranes. 36. A Simple, General Synthesis of Alkynyl Ketones1 and [E]‐1,3‐Alkenynes via Thexylchloroborane‐Dimethyl Sulfide
Authors: Brown Herbert C. , Bhat N. G. , Basavaiah D. 
Published: November 2013

AbstractThexylchloroborane‐dimethyl sulfide (1) hydroborates representative 1‐bromo‐1‐alkynes in the presence of 10% boron tribromide as a catalyst to afford thexyl‐(cis‐1‐bromo‐1‐alkenyl)‐chloroboranes (2). Treatment of these intermediates with isopropyl alcohol provides the corresponding isopropyl thexyl(cis‐1‐bromo‐1‐alkenyl)borinates (3B). Subsequent treatment with alkynyllithium gives the corresponding “ate” complexes (4) which undergo intramolecular migration of the alkynyl group from boron to the adjacent carbon, displacing the bromine, producing the corresponding cis‐vinylboranes (5). These intermediates (5) provide the corresponding alkynyl ketones (6) on oxidation and the corresponding stereodefined conjugated enynes (7) of high isomeric purity on protonolysis. Yields in the range of 60–65% were realized.
Cyclic Carboalumination of Alkynylsilanes Forming Exocyclic Alkenes
Authors: Miller Joseph A. , Negishi Ei‐Ichi 
Published: November 2013

AbstractThe reaction of 6‐trimethylsilylhex‐1‐en‐5‐yne with i‐Bu3Al (1.1 equivalents) and a catalytic amount of Cl2ZrCp2 in 1,2‐dichloroethane or CH2Cl2 at room temperature produces, after protonolysis, trimethylsilylmethylenecyclopentane in 85% yield. Upon iodinolysis of the reaction mixture, the corresponding iodide is obtained in 68% yield. Under the same reaction conditions, 7‐trimethylsilylhept‐1‐en‐6‐yne is converted into trimethylsilylmethylenecyclohexane in 72% yield upon protonolysis of the reaction mixture. Attempts to produce four‐ or seven‐membered ring compounds have not been successful. The i‐Bu3Al–Cl2ZrCp2 reaction of 6‐trimethylsilyl‐4‐methylhex‐1‐en‐5‐yne is nonstereoselective. However, the use of I2ZrCp2 in place of Cl2ZrCp2 improves the E/Z ratio to ca 80/20. The reaction of 1‐trimethylsilylhex‐5‐en‐1‐yn‐3‐ol with i‐Bu3Al–Cl2ZrCp2 gives the ca 90% pure Z isomer under “kinetic” conditions and the ca 97% E isomer under thermally equilibrating conditions in excellent yields.
Enantiocontrolled Synthesis of (R)‐3‐Substituted Cyclohexanones Using (S)‐2‐(p‐Tolylsulfinyl)‐2‐cyclohexenone and Various Organometallic Reagents in 2,5‐Dimethyltetrahydrofuran
Authors: Posner Gary H. , Frye Leah L. 
Published: November 2013

AbstractFour different (R)‐3‐substituted cyclohexanones of 65–96% enantiomeric purity have been prepared in 58–84% yields via organometallic conjugate additions to (S)‐2‐(p‐tolylsulfinyl)cyclohexenone in 2,5‐dimethyltetrahydrofuran (DMTHF) as a solvent which allows more effective metal ion chelation by the bidentate β‐ketosulfoxide (and therefore higher asymmetric induction) than does THF. Several recently‐reported organotitanium reagents have been used effectively for the first time as Michael donors.
Tricarbonyl(η6‐Cycloheptatriene)manganese Hexafluorophosphate: Reactions with Enolate Nucleophiles and Decomplexation of the Product Dienyl Complexes
Authors: Pearson Anthony J. , Bruhn Paul R. , Richards Ian C. 
Published: November 2013

AbstractReaction of tricarbonylcycloheptatrienemanganese hexafluorophosphate with a wide range of enolate nucleophiles derived from malonic esters, phenylsulfonylesters, β‐ketoesters and cyclohexanones proceeds cleanly to give 6‐substituted tricarbonyl(1–5‐η‐cycloheptadienyl)manganese complexes 3. It was found that demetallation with concomitant stereospecific hydroxylation, to give substituted cycloheptadienes, could be accomplished by direct treatment of the dienyl complexes with ceric ammonium nitrate in buffered wet acetone. Complexes 3a–3c gave mixtures of hydroxy esters and gamma lactones 6 and 7 in proportions which depended on the nature of the substituent present. A novel and potentially useful demetallative cyclofunctionalization was found to occur on treatment of hydroxy ester 3m with excess iodine in acetonitrile, to give the cyclic ether 10 as the only observable product.
Vinyl Ether–Iron Complexes as Vinyl Cation Equivalents. Preparation and Use of an α‐Acrylic Ester Cation Equivalent
Authors: Chang T. C. T. , Rosenblum M. 
Published: November 2013

AbstractThe organoiron complex 4 is readily prepared from α‐bromopyruvic ester diethyl acetal, and has been shown to serve as an effective α‐acrylic ester cation equivalent, in the synthesis of α‐methylene‐γ‐lactones. Cyclohexanone lithium enolate is transformed to either the cis or trans fused lactones 12c, t, and ethyl acetoacetate lithium enolate can be converted to the lactone 21t. The use of methyl 3‐oxohexadecanoate as starting material provides a stereospecific synthesis of protolichesterinic acid methyl ester.
Synthesis of Homoallyl Selenides and Sulfides by Allylation of α‐Seleno‐ and α ‐Thioalkyllithiums in the Presence of Copper(I) Salts
Authors: Clarembeau M. , Bertrand J. L. , Krief A. 
Published: November 2013

AbstractNew species, detected by 77Se NMR, are formed on mixing α‐selenoalkyllithium compounds and CuI/SMe2. These species decompose at −40° to olefins 8 but can be allylated in high yield at −100°. Similar reactions are observed with thio‐analogues.
General Synthetic Methods for the Preparation of 1,4‐ and 1,5‐Dicarbonyl Compounds. New Annulation Methods Based on the Palladium‐Catalyzed Oxidation of Terminal Olefins to Methyl Ketones
Authors: Tsuji Jiro , Shimizu Isao , Kobayashi Yuichi 
Published: November 2013

AbstractNew synthetic methods for the preparation of 1,4‐diketones, 4‐oxopentanals, and 5‐oxohexanals were developed based on the oxidation of terminal olefins to methyl ketones with PdCl2‐CuCl‐O2 as a key reaction. They constitute useful annulation methods.
The Status of the Photochemistry and Photophysics of Tritium‐From‐Deuterium Isotope Separation by Infrared Laser Multiple‐Photon Dissociation of Chloroform
Authors: Herman Irving P. , Magnotta Frank , Aldridge Frederick T. 
Published: November 2013

AbstractSeveral experiments that examine the multiple‐photon absorption and dissociation and the post‐photolysis chemistry of tritium‐from‐deuterium isotope separation by 12 μ laser photolysis of chloroform are described. Results of recent experimental measurements of T/D selectivity in absorption and dissociation are reviewed. The fluence dependence of CTCl3 IR photolysis is obtained from experiment and an energy‐averaged master equation model. Preliminary measurements of two‐frequency dissociation of CTCl3 are presented. The pathways of the post‐photolysis chemistry are deduced from product formation in the 11 μ dissociation of neat CDCl3, and of the carbon‐isotope labelled reactants 12CDCl3/13CHCl3.
Infrared Multiple Photon Absorption of Silicon Tetra‐Fluoride and Anisole
Authors: Haas Y. , Citri O. , Yahav G. 
Published: November 2013

AbstractThe infrared multiple absorption probabilities of the title molecules are measured at two frequency ranges: one for which the single photon absorption (SPA) cross section is large (range I), and another for which it is much smaller (range II). For SiF4, the high power absorption probability in range I is much smaller than the SPA cross section. Collisions significantly increase the average number of photons absorbed. In range II, the absorption cross section increases upon increasing the laser fluence. For anisole, the same fluence effect is qualitatively observed, but it is less pronounced in range I. For anisole pressure exceeding 0.1 torr collisions with argon do not change the average number of photons absorbed per molecule. The 10.2 μ absorption in SiF4 is suggested to be initiated by a single photon hot band absorption, followed by absorption in the quasi‐continuum (QC). QC absorption cross sections are in the range of (5–20) × 10−21 cm2 for both SiF4 and anisole.
A Quantitative Test of the Statistical Limit for Multiphoton Ionization‐Fragmentation
Authors: Ohmichi N. , Silberstein J. , Levine R. D. 
Published: November 2013

AbstractObserved ionic fragmentation patterns are compared against the extreme statistical limit. A quantitative measure of closeness of fit is employed to assess the need for refinements in the theory and in the noise level of the experiment. It is concluded that for such molecules as benzene or toluene there is no compelling reason to go beyond the extreme statistical limit in order to account for the observed fragmentation patterns. There is some indication for meaningful deviances in MPI‐D of aliphatic compounds.
On the Dynamics of Molecular Two‐Photon Excitation through Real Intermediate States
Authors: Bigio Laurence , Grant Edward R. 
Published: November 2013

AbstractNew results from our laboratory on the two‐photon absorption spectroscopy and photodissociation dynamics of NO2 are examined in the light of a simple nonperturbative theory for the time evolution of the intermediate state in a three‐level system. Experiments on NO2 show effects distinct to two‐photon excitation, evident spectroscopically in intense bent‐to‐linear origins and dynamically in unique patterns of energy disposal in two‐photon photodissociation. We trace these effects to intramolecular relaxation which can be described by the evolution of an intermediate wave packet composed of a superposition of vibronic states prepared by the absorption of the first photon. Our theoretical treatment addresses the timescale for this evolution. Its results suggest that this timescale will depnd on the intensity of the driving field, and so offer the intriguing possibility that the spectroscopy and dynamics of two‐photon excitation through a system of real states will depend on laser intensity in a manner that tracks the time dependence of the intermediate wave packet.
Multiphoton Ionization Photoelectron Spectroscopy
Authors: Reilly James P. 
Published: November 2013

AbstractRecent research involving the monitoring of photoelectrons generated in the course of molecular multiphoton ionization is reviewed. Information about the order of the multiphoton ionization process, the identity and ionization potential of the species ionized, and spectroscopic data about excited states of neutral molecules and the ground states of ions can all be extracted using this new technique.
Coherent Vacuum Ultraviolet in Chemical Physics
Authors: Hepburn J. W. 
Published: November 2013

AbstractMethods of generating coherent vacuum ultraviolet radiation by frequency mixing techniques are reviewed. The theory and methodology of four‐wave mixing in gas mixtures is discussed and some representative methods for generating coherent light in the range from 900 Å to 2000 Å are described. In the last section some recent applications of these VUV sources to chemical physics will be outlined.
Synthesis and Structures of Substrates for Investigation of Intramolecular Electronic Energy Transfer
Authors: Rubin Mordecai B. , Migdal Shmuel , Speiser Shammai , Kaftory Menahem 
Published: November 2013

AbstractA series of cyclic α‐diketones incorporating a benzene ring (ortho, meta or para substituted) have been synthesized for studies of intramolecular energy transfer (intra‐ET). The synthetic method involved acyloin cyclization of the corresponding dicarboxylic acid diesters followed by oxidation with DMSO‐acetic anhydride reagent. All compounds were sufficiently flexible so that, even at temperatures in the range of −120°, only broadened lines were observed in their NMR spectra, consistent with observations on temperature dependence of the intra‐ET process. The structure of one compound (P‐4,4) was established by X‐ray crystallographic analysis and of the remaining compounds by a combination of spectroscopic data and molecular mechanics calculations. The calculated structure of P‐4,4 is essentially identical to the X‐ray structure. In all compounds the methylene chains assume staggered conformations, the dicarbonyl torsion angle aproached 180°, and the molecule folds in such a way that, with one exception, the dicarbonyl moiety lies above (or below) the plane of the benzene ring. Distances between chromophores range from about 3.3 to 5.8 Å.
The Chemistry of Platinum in the +3 Oxidation State
Authors: O'Halloran Thomas V. , Lippard Stephen J. 
Published: November 2013

AbstractPlatinum(III) is no longer an uncommon oxidation state. Numerous binuclear platinum(III) complexes have been prepared and structurally characterized over the past eight years. These include sulfate‐bridged dimers of D4h symmetry, [Pt2(SO4)4L2]2−, L = H2O, DMSO; phosphate‐bridged complexes [Pt2(HPO4)4‐(H2O)2]2− and [Pt2(H2PO4)(HPO4)3(py)2]−; POP (H2 P2 O2−5)‐bridged ions [Pt2‐(POP)4X2]2−, X = halide; an extensive series of α‐pyridonate (C5H4NO−)‐bridged head‐to‐head and head‐to‐tail complexes, [Pt2(NH3)4 (C5H4NO)2XY]n−, X, Y = NO3, NO2, H2O, Cl, Br; n = 2, 3; and organometallic derivatives such as [Pt2(CH3)4‐(CF3CO2)2(4‐Mepy)2]. In all cases there is a Pt–Pt single bond of length 2.47–2.7 Å, pseudo‐octahedral geometry about platinum, and two or more bridging ligands. The complexes are stable in solution and some undergo quasi‐reversible two‐electron redox reactions. Mononuclear platinum(III) complexes are less well characterized structurally, but have been stabilized in diamagnetic host lattices in the solid state and by macrobicyclic cage ligands in solution following pulse radiolytic or γ‐irradiation of precursor platinum(II) complexes. The first unequivocal, crystallographically characterized mononuclear platinum(III) complex, [Pt(C6Cl5)4]−, has just been reported.
Metalloporphyrins in Oxidative Catalysis. Oxygen Transfer Reactions of Oxochromium Porphyrins
Authors: Groves John T. , Kruper William J. 
Published: November 2013

AbstractThe oxidation of chloro‐5‐10,15,20‐tetramesitylporphyrinotoiron(III) with peroxyacids affords a reactive oxoiron(IV)‐porphyrin cation radical species 2. The characterization of 2 and its oxochromium analogs 3, 4 and 5 are reviewed. The nature of reactive oxochromium species derived from chromyl reagents is also reviewed. The oxidation of triphenylphosphine by CrOTPP (11), CrOTTP (13) and CrOTMP (14) is described. Variations in the rate constants indicate that steric factors affect the rate of oxygen atom transfer. Activation parameters for the oxidation of triphenylphosphine by 14 are ΔH≠ = 6.96 kcal/mol and ΔS≠ = −39 eu. The oxidation of t‐butylphenylcarbinol (18) by CrOTPP gave predominantly benzaldehyde via carbon—carbon bond cleavage while the chromium(III) porphyrin‐catalyzed oxidation of 18 by iodosylbenzene afforded t‐butylphenylketone.
Complexes of Hydrogen Peroxide with Dioxoactinide(VI) Species in Aqueous Carbonate and Bicarbonate Media. Formation of An(VI)–H2O2 Complexes
Authors: Thompson Mary E. , Nash Kenneth L. , Sullivan James C. 
Published: November 2013

AbstractThe spectra for 1:1 complexes formed between triscarbonatouranium(VI) + H2O2 and triscarbanatoneptunium(VI) + H2O2 are presented. The respective rates of formation (25°C, 0.05 M NA2CO3) are 565 ± 41 M−1 s−1 and (2.19 ± .01) X 103 M−1 s−1. The corresponding activation parameters are ΔH* = 67.8 ± 3.2 kJ/m, 43.6 ± 2.0 kJ/m, ΔS* = 30 ± 11 J/m °K and −36 ± 7 J/m °K, respectively. The U(VI) complex appears to be stable over a period of months while the Np(VI) complex is formed as a transient species that disappears via a complex process.
Pulse and Continuous Radiolyses of the Europium and Neodymium Decatungstate Anions in Aqueous Solution
Authors: Mulazzani Quinto G. , Venturi Margherita , Ballardini Roberto , Gandolfi Maria T. , Balzani Vincenzo 
Published: November 2013

AbstractWe have studied the behavior of aqueous solutions of the [M(3+)(W5‐O18(6‐))2]9− complexes (M = Eu or Nd) under pulse and continuous radiolysis conditions. Both complexes react with e−aq at a diffusion controlled rate. For the Nd3+ complex in solution containing 1% 2‐propanol, the decay of the e−aq absorption was accompanied by the formation of a broad absorption band in the visible (λmax 600–650 nm), with a further increase in absorption up to 2 ms. For the Eu3+ complex under the same conditions, the decay of the e−aq absorption was accompanied by the formation of an absorption maximum at ∼370 nm, which is characteristic of Eu2+ species. On a longer time scale, a relatively intense absorption arose in the visible (λmax 600–650 nm) according to a complicated kinetic behavior. The two complexes exhibited a quite similar behavior in continuous radiolysis experiments. Blue products (λmax 600–650 nm) were formed and, for the Eu3+ complex, the disappearance of the Eu3+ emission was observed. Even after high irradiation doses, the absorption (and, for Eu3+, emission) spectra of the solutions were quantitatively regenerated by air oxidation. The behavior of the Nd3+ complex is interpreted on the basis of the reduction of a W5 O186− ligand by e−aq and alcohol radicals, followed by protonation. For the Eu3+ complex, the reduction by e−aq causes mainly the formation of a Eu2+ complex. On a longer time scale, protonation and/or reaction with alcohol radicals drive back the electron from Eu2+ to the W5O186− ligands, with formation of stable blue products.