A spectroscopic study to interpret the increased piezoelectric effect at high temperature in poly(vinylidene fluoride)

Spectroscopic experiments were carried out to directly measure the electric-field-induced microstructural changes in PVF₂ at high temperature (65°C). We found, in comparison with roomtemperature measurements, that the reduction of the coercive field is directly related to faster dipolar orientation at this temperature. Furthermore, the α to β or δ phase transformation can take place at a much faster rate and lower field strength than has been previously reported either theoretically experimentally.     

A contradistinction in the magnetic (13C NMR spectroscopy) and chemical behaviour of 4-Oxo-4,5,6,7-tetrahydroindole derivatives

Carbon-13 NMR data are reported for a series of 1,2-diaryl-4-oxo-4,5,6,7-tetrahydroindoles, 6-methyl-2-phenyl-4-oxo-4,5,6,7-tetrahydrobenzofuran and 1-,6-dithiaindan-4-one. The chemical shifts δ 193–196, δ 195.5 and δ 184 are identified for the carbonyl carbon (C-4) in the tetrahydroindoles, tetrahydrobenzofuran and dithiaindan derivatives, respectively. These shifts are located in the same region as that reported for the corresponding carbonyl carbon in aryl conjugated ketones. An excellent correlation between the chemical shift for the carbonyl carbon and the chemical reactivity of the ketonic function is noticed in the case of the latter two series of ketones while such a correlation is typically absent in the case of the 4-ketotetrahydroindole derivatives.     

Thermally-Induced Phase Transitions in the Uniaxially-Oriented δ Form of Syndiotactic Polystyrene

The empty δ (δ_e) form of uniaxially-oriented syndiotactic polystyrene (sPS) samples were obtained by extracting the solvent molecules from the δ form of sPS and solvent complex in acetone and methanol. Temperature dependence of the X-ray fiber diagrams starting from the uniaxially-oriented δ_e and δ form has been measured successfully at various temperatures for the first time. The transition behavior was traced clearly by separating the equatorial and layer line reflections. The δ_e form transformed to the γ form via an intermediate form. The intermediate form is speculated to take disordered structure due to the empty cavities present in the δ_e form. Calorimetric studies showed an endotherm followed by an exotherm during this phase transition, which is consistant with such a speculation. On the other hand the δ form transformed to the γ form directly without passing through the intermediate form or δ_e form. During the δ to γ phase transition the solvent molecules evaporate through the columnar structure in a broad range of temperature, allowing the transition to occur smoothly.     

Vapor sorption in emptied clathrate samples of syndiotactic polystyrene

The analysis of chloroform vapor sorption at 35°C in semicrystalline syndiotactic polystyrene samples shows remarkably different sorption isotherms, depending on the crystalline form of the samples. In particular, “emptied” clathrate (“emptied” δ form) samples are characterized by higher equilibrium sorption levels and the differences are particularly relevant for low vapor activities. Moreover, sorption kinetics detected at a vapor activity equal to 0.5 show that in the case of “emptied” δ form samples the sorption rate is much higher than for the other semicrystalline samples. The larger sorption equilibrium uptakes and sorption rates of the “emptied” δ form samples are essentially due to their ability to absorb chloroform, already for low activities, by clathration in the crystalline phase. The measured equilibrium uptakes and sorption kinetics suggest that “emptied” δ form samples of syndiotactic polystyrene could be suitable for removing polluting chlorinated compounds from vapor and liquid streams. © 1997 John Wiley & Sons, Inc.     

A correlation between isomer shifts of237Np Mössbauer spectra and coordination numbers of Np atoms in neptunyl(V) compounds

Five neptunyl(V) compounds were synthesized and studied by²³⁷Np Mössbauer spectroscopy. The isomer shifts (δ) of the Mössbauer spectra ranged from ?18.6 to ?19.1 mm/s for the compounds with Np atoms surrounded by 7 oxygen atoms (coordination number (CN) 7). On the other hand, the larger value of δ was obtained for the compound with CN 8. from the comparison of the present results with those reported on neptunyl(V) and (VI) compounds, it is concluded that there is a correlation between the δ and the CN for neptunyl(V) compounds, and the distribution of δ is narrower for neptunyl(V) compounds than that of neptunyl(VI) compounds.     

Effect of milled fluidised bed cracking catalyst waste on hydration of calcium aluminate cement and formation of binder structure

The effect of Bi addition on precipitation and dissolution, in Cu–9at% In and Cu–5at% Sb supersaturated solid solutions, has been studied by several complementary techniques. Differential Dilatometry and Differential Scanning Calorimetry permit only the analysis of the δ phase dissolution kinetic in sufficiently aged samples. Delayed spheroidization due to Bi segregation around the precipitated lamellae, observed by Transmission Electron Microscopies in the first alloy, gives a residual interfacial energy leading to accelerated δ phase dissolution with decreased activation energy. Kinetics parameters evolution indicates a progressive δ phase continuous dissolution which makes available a small chemical driving force at high temperatures and leads to an increasing activation energy during dissolution. However, Bi dispersed particles in the second alloy haven’t effect on the dissolution but they cause a contraction above 833 K. Kinetics parameters evolution indicates rapid δ phase dissolution that shifted to high temperatures where an important chemical driving force for solution treatment is available. It leads to almost constant activation energy.

     

Pterobiline and neopterobilines, reactivity and structures (author's transl)]

Pterobiline and neopterobilines, reactivity and structures Pterobiline (biliverdine IX γ) and the two neopterobilines: phorcabiline and sarpedobiline, are the three main bile pigments found in Lepidopters. Studies on the reactivity of pterobiline ( 1 ) and phorcabiline esters are reported. Preparation of derivatives, in vitro transformation of pterobiline into phorcabiline, analysis of the pigments and their derivatives by field desorption mass spectrometry and Fourier transform NMR., lead to the structure 5 for the dimethyl ester of phorcabiline. By a similar reaction, biliverdine IX δ ( 15 ) affords the neobiliverdine IX δ ( 16 ). Possibility of an easy formation of new tetrapyrrolic compounds in the IX γ and IX δ series is thus reported for the first time.     

Interpretation of isomer shift-quadrupole splitting correlations for pentacoordinate trimethyltin complexes

Linear correlations between ¹¹⁹Sn isomer shifts δ and quadrupole coupling constants e²qQ are noted for several series of pentacoordinate trimethyltin derivatives. The sign of the gradient of a δ versus e²qQ plot is interpreted as indicating whether the predominant effect on δ in a given series arises from rehybridization of the tin bonding orbitals or from a p-electron deshielding mechanism. Differences in magnitudes of the slopes are related to differences in the fractional s-character of the bonds between tin and the axial substituents.     

1H-, 13C- UND 77SE-NMR-STUDIE AN SCHWEFEL- UND SELEN-HALTIGEN CYCLISCHEN 6π-KATIONEN

Abstract

The ¹H, ¹³C and ⁷⁷Se NMR chemical shifts for 1,3-dithiolium, 1,3-thiaselenolium and 1,3-diselenolium tetrafluoroborates which are unsubstituted in the 4 and 5 positions and are unsubstituted or contain ethylseleno, ethylthio or morpholino groups in the 2 positions are reported. The dependence of the chemical shifts on the substituents and ring hetero atoms are discussed and shift increments given. The study includes the ¹³C shift effects for the following series of compounds: (a) thiotropone, ethylthiotropylium cation and tropylium cation; the iso-π-electronic heterocycles (b) thiopyrane-2-thione, 2-ethyl-thiothiopyrylium cation and the thiopyrylium cation, (c) 1,2-dithiole-3-thione, 3-ethylthio-1,2-dithiolium cation and the 1,2-dithiolium cation, and (d) 1,3-dithiole-2-thione, 2-ethylthio-1,3-dithiolium cation and the 1,3-dithiolium cation. Linear correlations between δ (¹H) and δ (¹³C), δ (⁷⁷Se) and δ (¹³C) and δ (¹³C) and δ (¹³C) (i) of neighbouring ring positions and (ii) between ring and substituent atoms proves, that changes in the electron density distribution of the ring systems is the intrinsic reason for the shift effects discussed. In particular the ⁷⁷Se/¹³C shift correlations show, that δ (⁷⁷Se) of double coordinated selenium atoms is determined by the 〈r ^?3〉_4p term in the contribution of paramagnetic screening σ_p(⁷⁷Se).

Es werden die ¹H-,¹³C- und ⁷⁷Se-NMR-chemischen Verschiebungen der in 4/5-Position unsubstituierten 1,3-Dithiolium-, 1,3-Thiaselenolium- und 1,3-Diselenolium-tetrafluoroborate, die in 2-Stellung unsubstituiert sind bzw. den Ethylseleno-, Ethylthio- oder Morpholinrest tragen, mitgeteilt und in Abhängigkeit von den Substituenten und den Ring-Heteroatomen diskutiert.

In die Betrachtung einbezogen sind die ¹³C-Verschiebungseffekte beim Übergang von den Thionen über die SEt-substituierten Kationen zu den Kation-Grundverbindungen in der Reihe Thiotropon/Ethyl-thiotropyliumion/Tropyliumion und der jeweiligen iso-π-elektronischen Schwefelheterocyclen Thiopyran-2-thion/2-Ethylthiothiopyryliumion/Thiopyryliumion, 1,2-Dithiol-3-thion/3-Ethylthio-1,2-dithioliumion/1,2-Dithioliumion und 1,3-Dithiol-2-thion/2-Ethylthio-1,3-dithioliumion/1,3-Dithioliumion.

Aufgefundene lineare Korrelationen zwischen δ (¹H) und δ (¹³C), δ (⁷⁷Se) und δ (¹³C) sowie δ (¹³C) und δ (¹³C) sowohl benachbarter Ringpositionen als auch zwischen Ring- und Substituentenatomen beweisen, daß als Ursache der diskutierten Verschiebungseffekte im Wesentlichen Änderungen der Elektronendichteverteilung der Ringsysteme anzusehen sind. Speziell die ⁷⁷Se/¹³C-Verschiebungskorrelationen zeigen, daß für δ (⁷⁷Se) zweifach koordinierter Selenatome der 〈r ^?3〉_4p-Term im σ_p (⁷⁷Se)-Verschiebungsbeitrag entscheidend ist.     

Determination Rapide de la Configuration Cis Trans des Alcenes CH?CHCH? Utilisation des Complexes de Terres Rares

In Z? CH? CH?CH? Y compounds (Z or Y being an alkyl group) the ethylenic part of the spectra is often very complex and the ³J(H? C?C? H) coupling constant which is a good tool for determining the configuration, is not easily determined. We have studied such allylic derivatives and many configurations have been assigned through stereospecific synthesis. Except a very few cases, δ CH(Z) of the cis isomer is larger than δ CHZ of the trans isomer. In alcohols RCH?CH? CHOHR′ the stereoisomers behave differently in solutions with europium, praseodymium, holmium and dysprosium complexes. The spectra of the trans isomers remain strongly coupled but ³J(H? C?C? H) becomes easy to measure in the cis compounds.     

Molecular spectra and molecular structure of heterocyclic compounds. Infrared and near ultraviolet absorption spectra of pyridine N-oxide derivatives

The infrared and ultraviolet spectra of many pyridine N-oxide derivatives have been studied. Ultraviolet spectra show a strong solvent effect in going from aprotic to hydroxylic solvents due to strong hydrogen bonding. Values of δ H° for several systems CH₃OH/XPyNO in tetra-chloroethylene solution were evaluated by infrared techniques and a linear correlation δ H° vs. δ v OH has been found. Features of the infrared and ultraviolet characteristic absorption bands were also investigated.     

Carbon-13 NMR of quinone methides

The ¹³C NMR spectra of four ortho- and seven para-quinone methides were assigned using chemical shift and long-range carbon-proton coupling information. The carbonyl shifts are compared with those in ortho- and para-benzoquinones. The chemical shifts of the carbonyls of the p-quinone methides are observed at δ 186.2–186.4 for the three ortho-di-tert-butyl-substituted compounds and at δ 180.7–181.5 for the four ortho-oxy-substituted compounds. In the three o-quinone methides with meta, para-dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the one o-quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result of hydrogen bonding to the nearby hydroxyl.     

Comparative study of the polymorphic species of strontium and calcium formates. II. X-Ray diffraction

The existence, in the temperature range 20–400°C, of three polymorphic species α, β, and δ of strontium formate, and of four polymorphic species α, β, γ, and δ of calcium formate is established by the means of X-ray diffraction. Crystal lattices of all these varieties are given, and the temperature ranges for their existence have been precisely stated. The importance of the role played by water vapor traces on some polymorphic transitions is pointed out.     

Parametre de solubilite d'un polyurethanne de structure definie

The limiting swelling of a polyurethane of well defined structure was investigated in numerous solvents. It was found that the polymer dissolved for a very narrow range of solubility parameter (δ) values. The swelling in various solvent mixtures exhibits a sharp maximum for δ = 9.6±0.2. This value is suggested for δ of the polyurethane. Theoretical evaluations lead to a similar result. It was also found that for N-vinylpyrrolidone, a solvent for the polyurethane, δ is between 9.5 and 11.1.     

Effects of structural imperfections on the dynamic mechanical response of main-chain smectic elastomers

We examine the influence of structural imperfections on mechanical damping in polydomain smectic main-chain liquid crystalline elastomers (MCLCE) subjected to small strain oscillatory shear. The mechanical loss factor tan δ = G″(ω)/G′(ω) exhibits a strong maximum (tan δ ≈ 1.0) near the smectic-isotropic (clearing) transition. “Optimal” elastomers that exhibit minimal equilibrium swelling in a good solvent are compared with highly swelling “imperfect elastomers” that contain higher concentrations of structural imperfections such as pendant chains. For the imperfect elastomers, tan δ is markedly enhanced in the isotropic state because of relaxation of pendant chains and other imperfections. However, within the smectic state, the magnitude of tan δ and its temperature dependence are similar for optimal and imperfect elastomers at ω = 1 Hz. The prominent loss peak near the clearing transition arises from segment-level relaxations that are insensitive to the details of chain connectivity. Smectic MCLCE can be tailored for applications as vibration-damping materials by manipulating the clearing transition temperature through the backbone structure or by deliberate introduction of structural imperfections such as pendant chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3267–3276, 2007     

Azabicyclo chemistry. 7. Ultra-high field (600 MHz) NMR spectroscopy in solving conformational problems: cis-Octahydroindoles

Studies using ultra-high field (600 MHz) nmr spectroscopy has allowed us to assign the conformational preference of cis-octahydroindoles, including the position of their nitrogen lone-pair electrons. Lithium aluminum hydride reduction of cis-octahydroindol-2-one ( 4 ) gave cis-octahydroindole ( 5a ) which showed three distinct nmr resonances, the C7a proton at δ 3.04 (apparent q, J = 5.3 Hz) and the two C2 protons at δ 3.10 and 2.94. The latter two resonances were absent in the C2 deuterated compound 5b . Deuteromethylation of 5a , via a urethane intermediate, gave 1-deuteromethyl-cis-octahydroindole ( 8a ) which showed resonances at δ 3.12 for the α-faced C2 proton, the β-faced C2 proton at δ 2.17, and the C7a proton at δ 2.15. The resonances at δ 3.12 and 2.17 are absent in the corresponding C2 deuterated compound 8b , and the C7a remains as a doublet of triplets (d, J = 5.5 Hz; t, J = 3.8 Hz). Interpretation of the above data led us to assign 8a as the cis compound with nitrogen axial, and the lone pair electrons in a pseudo-axial position and antiperiplanar to the C7a and β-faced C2 protons. The amine 5a is also cis and has the nitrogen axial, but the lone pair electrons are pseudo-equatorial. Inspection of the Bohlmann band region in the ir of 5a and 8a supports the above assignments. These investigations thus suggest, in cis-octahydroindoles, the following steric order: methyl > lone pair > H.     

High-temperature transport in perovskite-type Ca0.25Sr0.75Fe0.75Mo0.25O3 − δ

Journal of Solid State Electrochemistry - The comparative study of transport characteristics of SrFe0.75Mo0.25O3 − δ and Ca0.25Sr0.75Fe0.75Mo0.25O3 − δ was carried out in...     

Interactions of volatile organic compounds with syndiotactic polystyrene crystalline nanocavities

The interaction of some volatile organic compounds, namely, 1,2-dichloroethane, 1,2-dibromoethane, and 1,1,2,2-tetrachloroethane, included in the δ crystalline phase of syndiotactic polystyrene (sPS) has been studied in terms of conformation, orientation, and dynamical behavior. By combination of X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and solid-state (2)H NMR analyses, it has been shown that despite the differences in guest molecular properties (mass, boiling temperature, and volume), stable sPS/guest δ-clathrate cocrystals are formed since the nanoporous δ crystalline form has a flexible structure able to adapt itself to the guest molecule. As a consequence of inclusion, it has been shown that the guest diffusivity is strongly reduced and the dynamical processes are constrained, particularly when these guests are in trans conformation. This suggests the nanoporous sPS δ form to be an efficient tool for water and air purification through volatile organic compound absorption.     

Zersetzungsdrücke und Phasengrenzen von Niobnitriden

Dissociation Pressures and Phase Boundaries of Niobium Nitrides Dissociation pressures of niobium nitrides in the region NbN_1.006–NbN_0.45 were measured by a thermogravimetric method at temperatures from 1300 to 1800°C. The results enabled us to make statements on the two phase regions η/δ, δ/γ and δ/β and on the homogeneity ranges of the δ and the β phase. Enthalpies of the conversions η → δ, δ → γ, δ(γ) → β, and of the formation of the δ phase were calculated. A partial three dimensional c,p,T diagram and a proposal for a twodimensional c,T diagram of the Nb? N system have been designed.     

Infrared and MAS NMR Spectroscopic Studies of Al18B4O33

IntroductionAllsB.O,, is a refractory compound with the melting point of 1 713 K. It has a low density of 2. 94 g/cm' and tends to form a needle--shaped crystal. These characteristics lead to itspotential application in reinforced plastics or metal alloys['j. The investigationL'] in the crystalstructure Of Al,SB,O,, by X-ray study has reve.aled that the material has a 10Al,O,. BZO3type structure. This structure contains AIO.--tetrahedra, AIO,-octahedra, five-oxygen-coordinated Al ato…