Perfluorocycloalkyl(aryl) diazenes from heptafluoronitrosocyclobutane and nonafluoronitrosocyclopentane

The perfluoronitrosocycloalkanes, heptafluoronitrosocyclobutane and nonafluoronitrosocyclopentane, are convenient precursors to a family of new perfluorocycloalkyl(aryl) diazenes. With aniline and o-aminobenzamide, $\text{CF}{}_2\text{(CF}{}_2\text{)}{}_{\mathrm{x}}\text{C}$FNN$\text{C(CH)}{}_4\text{C}$H and $\text{CF}{}_2\text{(CF}{}_2\text{)}{}_{\mathrm{x}}\text{C}$FNN$\text{C(CH)}{}_4\text{C}$C(O)NH₂ (x = 2,3) are formed. Additionally, heptafluoronitrosocyclobutane gives $\text{CF}{}_2\text{(CF}{}_2\text{)}{}_2\text{C}$FNN$\text{CCFCFCHCFC}$F and $\text{CF}{}_2\text{(CF}{}_2\text{)}{}_2\text{C}$FNN$\text{C(CH)}{}_4\text{C}$NH₂ with 2,3,5,6-tetrafluoroaniline and o-phenylenediamine     

Proprietes dielectriques d'une serie de polyoxyethylene (POE) presentant des masses moleculaires lentement variables (200 ≤ Mw ≤ 4 × 106)

In this paper, we present dielectric results for samples of POE (polyethyleneoxyde) divided into three classes. Compounds of low molecular weight ($\text{M}{}_{\mathrm{w}}\text{< 1000}$) show very weak absorption at lower temperatures. At higher temperatures (below the melting point), there appears a very important peak (stronger for lower $\text{M}{}_{\mathrm{w}}$) which corresponds to the supercooled phase. Compounds of intermediate molecular weight ($\text{1000 ≤}\text{M}{}_{\mathrm{w}}\text{≤ 10}{}^5$) show a β relaxation near 250 K (bis$\text{M}{}_{\mathrm{w}}\text{? 3000}$) which is due to the movement of chain-ends in the amorphous phase. This process increases with the importance of that part of the structure formed of shorter lamellae, thus explaining the marked diminution of this absorption for higher molecular weight compounds (the shorter lamellae cannot be obtained for $\text{M}{}_{\mathrm{w}}\text{> 4000}$). The α relaxation (obtained for T > 300 K) is perturbed by an important conduction; however, we have found a peak and a shoulder at lower frequencies, due to shorter and longer lamellae respectively. The shoulder is also present for high molecular weight compounds ($\text{M}{}_{\mathrm{w}}\text{≥ 0.1–10}{}^6$). At lower temperatures, they display a very broad γ absorption, superposed at higher frequencies with a β relaxation. The nature of this β relaxation is different from that observed for the intermediate molecular weight compounds.     

Etude cristallochimique des phases de type perovskite du systeme Th0.25 NbO3NaNbO3

The compound Th_0.25 NbO₃ melts congruently at 1390°C. Single crystals obtained by slow cooling from the melt are transparent and show uniaxial optical properties. A single-crystal X-ray analysis confirms the tetragonal cell found by Kovba and Trunov from a powder data and gives a = 3.90 Å and c = 7.85 Å. No systematic absence of the hkl reflections is observed on precession films. The relative intensities of the main reflections are characteristic of a perovskite-like arrangement ABO₃ whose large dodecahedral A sites are only partly occupied. Several domains have been found in the perovskite-type solid solution (1 ? x) Th_0.25NbO₃-x NaNbO₃. For 0 ? x ? 0.5 the phases have a tetragonal cell with $\text{a ? a}{}_0$ and $\text{c ? 2a}{}_0$ as in pure Th_0.25 NbO₃. When 0.6 ? x ? 0.8 the corresponding phases crystallize with a small cubic cell ($\text{a}{}_0\text{? 3.9}$Å), while phases with 0.9 ? x ? 1 have an orthorhombic cell ($\text{a ? 2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{a}{}_0\text{, b ? 2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{a}{}_0\text{, c ? a}{}_0$).     

On the kinetics of polymer degradation in solution—IV: Laser flash photolysis studies on copolymers containing phenylvinylketone using the light scattering detection method

Copolymers of methylmethacrylate (MMA) with phenylvinylketone (PVK) and of styrene (St) with PVK were degraded in solution by irradiation with 25 nsec flashes of 347.1 nm light from a ruby laser. The time dependence of the change of light-scattering intensity (LSI) (due to the decrease of molecular weight) was measured. It was found that the half-life $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) decreases with increasing polymer concentration according to [($\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(LSI)}\text{]}{}^{\mathrm{?1}}\text{∝ C}{}_{\mathrm{<mtext>Polymer</mtext>}}$ and that $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) is proportional to the microviscosity (viscosity of the solvent). This was taken as evidence that $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) corresponds to a diffusion process. $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) decreased with increasing scattering angle, explained by the fact that at low scattering angles the diffusion of long fragments was predominantly monitored.Upon addition of naphthalene to an acetone solution of a copolymer of MMA and PVK, $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) increased with increasing naphthalene concentration and approached a limiting value. This effect was attributed to preferential solvation of the copolymer by naphthalene. From intrinsic viscosity measurements, it could be confirmed that MMA base units are preferentially solvated by an acetone/naphthalene mixture.     

Application of gel permeation chromatography and viscometry for characterization of branched polydisperse polycarbonate

Gel permeation chromatography (GPC) and viscometry (V) methods have been combined for determination of long-chain branching in bisphenol-A polycarbonate (PC) by means of a branching factor $\text{g}{}_{\mathrm{v}}\text{=}\text{M}{}_{\mathrm{vg}}{}^1\text{/}\text{M}{}_{\mathrm{v}}{}^1$, where $\text{M}{}_{\mathrm{vg}}{}^1$ and $\text{M}{}_{\mathrm{v}}{}^1$ are the apparent viscosity-average molecular weights calculated from GPC data and from intrinsic viscosities [η] of the samples respectively. A linear dependence of g_v on molar % of branching agent has been obtained. The GPC data on PC samples have also been applied for verification of an earlier [η]?M relationship for branched polydisperse polymers.     

Reaction de l'acetylene dicarboxylate d'ethyle avec l'oxo-6 (2H) cyclohepta (c) pyrrole ; mecanismes de formation des adduits

The cycloaddition reactions of 6-oxo (2H) cyclohepta (c) pyrroles $\text{4a, b and c}$ with diethyl acetylene dicarboxylate an electron-deficient dienophile of relatively low LUMO energy level, afford the 1:2 adducts $\text{5a, b}{}_1\text{-b}{}_2\text{and c}$ respectively The kinetics of the reactions, investigated By ¹H NMR spectroscopy, have allowed to precise the mechanism of the addition In particular, new-intermediates, 1:2' adducts $\text{6b and c}$ have been observed and isolated for the compound $\text{6c}$.     

Dilute and concentrated solutions of polystyrene in trans-decalin close to and far from the θ-temperature—II. Osmotic pressure measurements

Osmotic pressure measurements on polystyrene ($\text{M}{}_{\mathrm{n}}\text{= 396. 000}$) in trans-decalin for concentrations up to 140 kg m^?3 and from 20 to 40 are reported. The θ-temperature is 20.8 . The ratio

where c⁺ is the concentration at which a homogeneous segment distribution is assumed to prevail, increases with temperature up to the plateau value of 0.7. From the temperature dependence of the osmotic pressure, the partial molar enthalpy. Δh₁, and entropy, Δs₁. of mixing are found to be positive. The solvent-solute interaction parameter increases linearly with concentration at all temperatures.     

Energy transfer between Gd3+ and Sm3+ the effect of Gd3+ on quenching of Sm3+ and intensity parameters of Sm3+ in borate glasses

Intensity parameters of Sm³⁺ in borate glasses were obtained by fitting the oscillator strengths to the Judd-Ofelt formula and a study of energy transfer from gadolinium to samarium was performed. An increase of samarium fluorescence originating from the ${}^4\text{G}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ level was observed in the presence of gadolinium, in the concentration range of 0.1–3 wt% samarium with gadolinium constant at 3 wt%. The intensity of samarium fluorescence on excitation at 273 nm increased by one order of magnitude in the presence of gadolinium. From the excitation spectrum of the double-doped glasses (Gd + Sm), it was deduced that energy absorbed by gadolinium is transferred from ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ gadolinium levels to the ${}^4\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and ${}^4\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ samarium levels.The mechanism of this energy transfer was obtained by plotting the energy transfer probabilities as a function of samarium concentration. A linear dependence of $\text{η}{}_0\text{η}$ (η intensity of gadolinium in the presence of samarium) versus square of concentration of Sm + Gd is obtained. From this it is concluded that the transfer is of electric-multipolar type, mainly dipole-dipole. A small increase (about 10%) of fluorescence of samarium in the presence of gadolinium excited at levels where no energy transfer can take place is attributed to the fact that the quenching of samarium occurring by the cross relaxation $\text{(}{}^4\text{G}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{→}{}^6\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{) (}{}^6\text{H}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{→}{}^6\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}$ is suppressed by the presence of gadolinium as seen from concentration dependence of samarium doped glasses compared to double-doped glasses.     

A dynamic nuclear magnetic resonance study of 1,3-intramolecular shifts in pentacarbonyl-chromium(O) and -tungsten(O) complexes of β-2,4,6-trimethyl-1,3,5-trithian, 1,3,5-trithian, 1,3-dithian and 2-methyl-1,3-dithian: the x-ray crystal structure of [W(CO)5{SCH(Me)SCH(Me)SCH(Me)}]

Variable temperature ¹H NMR spectroscopy has been used in the study of 1,3-intramolecular shifts of the M(CO)₅ moiety in complexes of the general formula [M(CO)₅L], (M = Cr or w), L = $\text{SCH}{}_2\text{SCH}{}_2\text{SC}$H₂, $\text{SCH}{}_2\text{SCH}{}_2\text{CH}{}_2\text{C}$H₂ and $\text{SCH(Me)SCH}{}_2\text{CH}{}_2\text{C}$H₂. For the 1,3,5-trithian complexes precise energy barriers for the process have been obtained by detailed computer simulation of the static and dynamic spectra. Our results suggest that the magnitude of ΔG^≠ (298.15 K) for the 1,3-shift is largely dependent upon the skeletal flexibility of the ligand system. In this context we have investigated the X-ray crystal structure of the highly substituted trithian complex [W(CO)₅{β-$\text{SCH(Me)SCH(Me)SC}$H(Me)}].     

Etude des volumes specifiques partiels de polystyrenes-modeles—Influence de la masse moleculaire et de la nature des groupements terminaux

It is well known that the apparent specific volume η₂ of a polymer may be expressed by the following relationship: $\text{η}{}_2\text{= η}{}_{\mathrm{m}}\text{+ K/}\text{M}{}_{\mathrm{n}}$ where M?_n is the number-average molecular weight of the polymer, η_m the specific volume of the infinite polymer, and K a constant. We have shown that this relationship is valid for low molecular weight polystyrenes ($\text{M}{}_{\mathrm{n}}\text{< 4·10}{}^4$) with different end-groups, independently of the nature of the solvent. The K values (and variations with the solvent and with the nature of the end-groups) may be predicted through simple calculations proposed here. We conclude that η_m does not represent the specific volume of the infinite polymer, since we observe a rapid decrease of η₂ for increasing M (when $\text{M}{}_{\mathrm{n}}\text{< 4·10}{}^4$). The decrease is much greater than expected from the relationship $\text{η}{}_2\text{= ? (1/}\text{M}\text{)}$.     

Optical and structural investigation of the lanthanum β-alumina phase doped with europium

The lanthanum β-alumina phase doped with europium was investigated by X-ray diffraction and fluorescence. This nonstoichiometric phase exists over the composition range: $\text{11}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$ to $\text{14}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$. The unit cell is hexagonal hexagonal with a = 5.560 ± 0.003 Å, c = 22.001 ± 0.003 Å and belongs to the $\text{P6}{}_3\text{mmc}$ space group. X-ray diffraction patterns do not vary between both boundary compositions, but fluorescence spectra show that the structure of the mirror plane in which the lanthanide ions are located is deeply modified. The atomic structure of the mirror plane is of “β-type” (like β(Na) or β(Ag)) for the lower alumina contents; it gradually changes to a “magnetoplumbite type” for higher alumina contents.     

Crystal structure,Mössbauer,and magnetic behavior of mixed valence compounds in the BaFeS system: Ba3(Ba1−xAlx)Fe2S6[S1−y(S2)y]

The compounds $\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{[S}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{S}{}_2\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{]}$ and Ba_3.6Al_0.4Fe₂S₆[S_0.6(S₂)_0.4], designated I and II, were prepared by reacting BaS, Fe, and S powders and Al foils in graphite containers sealed in evacuated quartz ampoules at approximately 1100°C. The crystal structure of I was determined using 1682 independent, nonzero X-ray reflections, while 3589 were used for II. They are triclinic, $\text{A}\text{l}$:

$\text{a=9.002(2)}\text{A}\text{?}\text{,b=6.7086(8)}\text{A}\text{?}\text{,c=24.658(4)}\text{A}\text{?}\text{α91.49(2)°,}$

$\text{β=105.10(2)°y=90.74(2)°,ψ}{}_{\mathrm{calc}}\text{=4.15g/cm}{}^3\text{,for I:}$

$\text{a=8.993(6)}\text{A}\text{?}\text{,b=6.708(7)}\text{A}\text{?}\text{,c=24.70(1)}\text{A}\text{?}\text{α91.11(6)°,}$

$\text{β=105.04(6)°y=90.90(9)°,ψ}{}_{\mathrm{calc}}\text{=3.90g/cm}{}^3\text{,for II:}$

BaS₆ trigonal prisms share edges to form distorted hexagonal rings which form one-dimensional chains leaving two free lateral edges. The chains link in a stairstep manner with the rings offset along the [301] direction. These stairsteps join in a complicated manner to form a three-dimensional network. Fe ions are in two sites forming isolated FeS₄ tetrahedra and isolated Fe₂S₆ dimers by edge-sharing tetrahedra. The Al substitution occurs in the trigonal prisms which have free edges with Al replacing Ba. Room-temperature Mössbauer isomer shifts are 0.20 mm/sec. for I and 0.30 mm/sec for II. These data indicate that upon Al substitution charge compensation occurs by reducing Fe³⁺. Valence calculations indicate that Fe in edge-sharing tetrahedra are reduced while the Fe in the isolated tetrahedron remains unchanged. The effective charge distribution in the Al substituted compound is approximately Fe³⁺, Fe^2.5+ with electron delocalization across the shared edge. Room temperature electrical resistivity is 10⁵ ohm/cm. The compositions of the crystals are best represented by the formulas $\text{[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_7\text{]}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{·[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{(S}{}_2\text{)]}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ and [Ba₃AlFe₂S₇]_0.4·[Ba₄Fe₂S₇]_0.2·[Ba₄Fe₂S₆(S₂)]_0.4. The replacement of a sulfide by a disulfide ion is thought to be strongly dependent on the sulfur activity during the preparation.     

Reactions of hydridosilacyclobutanes with low-valent complexes of iron or platinum

Unstable transition metal compounds formed from hydridosilacyclobutanes are described: 1-methyl-1-silacyclobutane reacts with nonacarbonyldiiron to give the complexes [Fe(CO)₄(H){$\text{Si(Me)CH}{}_2\text{CH}{}_2\text{C}$H₂}] and [$\text{Fe{CH}{}_2\text{CH}{}_2\text{CH}{}_2\text{Si}$(H)Me}(CO)₄], and with bis(triphenylphosphine)(ethylene)platinum(0) to give [Pt(H)(PPh₃)₂{$\text{Si(Me)CH}{}_2\text{CH}{}_2\text{C}$H₂}].     

Steric and kinetic effects of changing solvent and reactant in grignard reactions: Conformationally mobile versus rigid δ-keto esters

trans-7α-carbomethoxy-decal-1-one (2) yields a mixture of the two oxy-esters 6 and 7 on reacting with MeMgX. Ratios $\text{6}\text{7}$ were measured for reactions performed in benzene (with X = I) and in THF (with X = Cl). The small variations of the ratios $\text{6}\text{7}$ as compared to those obtained in analogous experiments performed with methyl (2-oxo-cyclohexyl)-propionate 4 and methyl 4-methyl-5-oxo-hexanoate 5 suggest that conformational mobility plays a fundamental role in determining the variations of stereospecificity with varying the reaction conditions. Competitive Grignard reactions among 2,4 and 5 show that their reactivities are in the order 4>2>5 ($\text{K}{}_4\text{k}{}_2$ = 1.7; $\text{k}{}_5\text{k}{}_2$=0.8) when reactions are performed in benzene with X  I and 2>4>5 ($\text{k}{}_4\text{k}{}_2$= 0.56; $\text{k}{}_5\text{k}{}_2$=0.25) when reactions are performed in THF with X  C1. The experimental data are interpreted in terms of anchimeric assistance given by the ester group to the reactions of the keto group in conformationally mobile δ-keto esters. The occurrence of this effect depends on the reaction conditions which can favour, or not, folded transition states.