Dielectric properties of poly(4-methylphenylisocyanate) and poly(4-methoxyphenylisocyanate) in solution

In the range 200 Hz-2 MHz, the dielectric behaviour of two polyarylisocyanates depends on the solvent. In certain solvents, such as toluene, there is only one high frequency absorption for poly(4-methylphenylisocyanate) and it is independent of molecular weight. Its character corresponds to chains having a low kinetic flexibility. In other solvents, this polymer, as well as poly(4-methoxyphenylisocyanate), shows two regions of dielectric absorption. The low frequency relaxation is molecular weight dependent: a polarization due to solvent polymer interactions occurs along the main chain. Despite its solvent-dependence, the total dipole moment of these polyarylisocyanates which behave like coils is much lower than that of polyalkylisocyanates, which are known to be rod-like.     

Conformational analysis of some (E)-α-phenyl-β-(2-thienyl)- and -(2-furyl_acrylic acids

NMR spectral data of some (E)-α-phenyl-β-(2-thienyl) acrylic acids indicate that these compounds exist in the preferred s-trans conformation. In the case of (E)-α-phenyl-β-(2-furyl)acrylic acids and their methyl esters the presence of only s-cis rotamer has been established.     

Synthesis of 3-[5-anilino-(2,3-d)-dioxole-1,3]-1-oxo-1,3-dihydro-2-benzofurane

A microscale synthesis (500 mg) of the product 3-[5-anilino-(2,3-d)-dioxole-1,3]-1-oxo-1, 3-dihydro-2-benzofurane (COR.01.126) is described. This method, which requires only four steps, is principally available for the ¹⁴C-labeled synthesis with labeled phthalic anhydride as starting material.     

Mechanistic studies on the photo-oxidation of commercial poly(butadiene)

Products from both the thermal and photo-oxidation of poly-butadiene have been studied using various analytical techniques such as infra-red and ultra-violet spectroscopy, gas-liquid chromatography and phosphorescence emission and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photo-oxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α, β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.     

Glass transition temperatures of poly(itaconic acid ester)s containing pendant cycloalkyl rings

A series of poly(itaconic acid ester)s with pendant cycloalkyl rings, ranging in size from cyclopropyl to cyclododecyl, have been prepared. Two distinct groups have been synthesized; Group I derivatives have the ring attached directly to the main chain through an oxycarbonyl group and Group II polymers have a methylene unit inserted between the ring and the oxycarbonyl group. The glass transition temperatures, T_g, have been measured for polymers in each group. In Group I, T_g increased with ring size up to the dicyclohexyl derivative, but it then decreased with further increase in ring size. The decrease in T_g is due to the inherent flexibility of the ring which leads to internal plasticization of the sample. This effect appears to predominate over ring size in determining the magnitude of T_g, for 7–12 membered rings. Similar trends have been found in the Group II polymers, but the effect of the ring becomes less important the further it is moved away from the chain backbone.     

Combustion of poly(1-methyl hexamethylene) and poly(1-methyl tetramethylene) and identification of the main decomposition products

The Bayer-ICI-Shell apparatus has been used to carry out combustion experiments on poly(1-methyl hexamethylene) (PH) and poly(1-methyl tetramethylene) (PT) using different air flow rates at various combustion temperatures. The products were adsorbed on charcoal followed by benzyl-alcohol desorption. They were separated and identified using gas chromatography.The non-oxidized products were identified as short chain, saturated and unsaturated hydrocarbons while the main oxidized products are short chain ketones and alcohols. The intensities of the chromatographic peaks of the separated products depend upon the temperatures and air flow rates in the combustion apparatus.     

Extractive photometric determination of gold(III) with 1-(2',4',6'-trichlorophenyl)-4,4,6-trimethyl-(1H,4H)-2-pyrimidinethiol in presence of tri-iso-octylamine

Tervalent gold was determined spectrophotometrically as its anionic 1:4 gold-thiol complex extracted into chloroform from aqueous acidic medium (1.5M sulphuric acid) in the presence of tri-iso-octylamine. The complex exhibits maximum absorption at 480 nm (molar absorptivity 4.60 x 10(3) l.mole(-1).cm(-1)) and Beer's law is obeyed in the concentration range 5-50 microg of gold(III) per ml. The relative standard deviation and relative error, calculated from ten determinations of solutions containing 15 microg of gold(III) per ml were 1.0% and 0.8%. The method is simple, selective and reproducible. It permits separation of gold(III) from associated elements and its determination in synthetic mixtures.     

A comparative study of lithium,sodium and hydrogen bonds formed by 1:1 interaction of electron donor molecules with lithium,sodium and hydrogen halides

Dissociation energies of 1:1 complexes of hydrogen, lithium and sodium halides with water, methanol and ammonia vary in the order LiX > NaX > HX, the dissociation energy in the case of lithium bonds being of the order of 200 kJ mol^?1 or more. The dissociation energy of sodium bonds lies in the range 80–120 kJ mol^?1. The magnitude of charge transfer, Δq, between the donor and acceptor molecules is also highest in the case of lithium bonds. The dissociation energies and Δq have been related with various properties of the complexes.     

The crystal structure of Cu4(PO4)2O

Cu₄(PO₄)₂O crystallizes in the space group $\text{P}\text{1}$ with a = 7.5393(8) Å, b = 8.1021(9) Å, c = 6.2764(8) Å, α = 113.65(1)°, β = 98.42(1)° and γ = 74.19(1)°. The structure was refined by full-matrix least-squares techniques using automatic diffractometer data to R = 0.046 (R_w = 0.056). Four unique copper atoms are in six, five-, and four-coordinated polyhedra which are linked together to form a three-dimensional network. The structure is best described in terms of a cubic close-packed array of oxygen atoms with one-tenth of the possible anion sites vacant.     

Solvent extraction and spectrophotometric determination of palladium(II) with some nitrogen-containing heterocyclic hydrazones in the presence of chloride ions

Three terdentate hydrazones, all containing the 1-phthalazino grouping in the hydrazine moiety but differing in the heterocyclic substituent in the aldehyde moiety, have been used as analytical reagents for palladium(II), the optimal conditions for the extractive spectrophotometric determination of palladium(II) in the presence of chloride ions being deduced. These compounds are highly selective and sensitive reagents for palladium(II), since they are not extracted into chloroform from sulfuric acid solutions and do not react with other platinum group metals. The desirable spectral properties of the palladium(II) complex of benzothiazole-2-aldehyde-1-phthalazinohydrazone (BAPhH) have also been discussed with respect to preference of the C  N structural form in the heterocyclic ring on the aldehyde moiety of the ligand.     

Itinerant electron ferromagnetism in Sr2+-, Ca2+-, and Ba2+-doped rare-earth orthocobaltites (Ln3+1−xM2+xCoO3)

Electronic and magnetic properties of Ln_1?xSr_xCoO₃ (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba²⁺ in LaCoO₃ favors itinerant electron ferromagnetism relative to Sr²⁺ while Ca²⁺ is less favorable than Sr²⁺.     

The unusual iron complex with a trimethylenemethane type ligand, (η5-cyclopentadienyldicarbonylmanganese)- (phenylmethylene)carbomethaneiron tricarbonyl [Cp(CO)2 MnC(CO)CHPh]Fe(CO)3

The binuclear complex with composition [Cp(CO)₂ MnC(CO)CHPh]Fe(CO)₃ is obtained by interaction of CpMn(CCHPh)(CO)₂ with Fe₂C0)₉. An X-ray study of this complex has shown that besides three carbonyl groups the iron atom is covalently bonded to four atoms, viz. the carbon of a phenylmethylene group, the carbon of a bridging CO group, the manganese atom and the central carbon of the organomanganese ligand lying just above iron. It seems to be the first example of a heteroatomic analogue of trimethylenemethane complexes.     

Spectrophotometric study of the copper(II)-2,2′-dipyridyl-2-pyridylhydrazone complex formation

The reaction of copper(II) ions with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) has been studied. Two copper complexes were found to be formed. One at pH 6.5 to 8.5 and the other at pH 11.9 to 12.6 with molecular extinction coefficients of 1.9 × 10⁴M^?1 · cm^?1 at the absorption maximum of 478 nm and 3.8 × 10⁴M^?1 · cm^?1 at 448 nm, respectively. A sensitive spectrophotometric procedure for the determination of copper at less than a 1-ppm level is proposed.     

1H and 13C NMR study of the conformations of the atropisomers of some 1-(11-naphthyl)-2,4-dioxo-(or 2-thio-4-oxo)-hexahydro-pyriminides

The ¹H and ¹³C NMR spectra of the atropisomers of 6-(or 5-)-methyl-1-(1¹-naphthyl)-2, 4-dioxo-(or 2-thio-4-oxo)-hexahydro-pyrimidines, 1 to 4, are assigned on the basis of NOE and double resonance experiments. The syn-anti configurations of the isomers of 6-methyl-2,4-dioxo-pyrimidine follow from the close similarity of the NMR parameters to those observed with the isomers of the 6-methyl-2-thio derivative of known configuration. That of the 5-methyl derivatives was assigned from NOE and magnetic anisotropy effects of the naphthalene ring and of the (thio) amide group. Allylic strain between the naphthyl and 5-methyl groups makes the axial confomation prefered int he anti isomers. In the syn isomers, however, the equational and axial conformations are approximately equally populated, apparently due to interference between the remote benzene ring and the axial methyl group. The equatorial conformation is prepared with the 5-methyl derivatives.     

Coordination behaviour of benzothiazolines towards stannous ion

Equimolar reactions of tin(II) methoxide with benzothiazolines result in the isolation of a new series of tin(II) complexes, which further undergo 1:1 adduct formation with pyridine. The electronic, IR and ¹H NMR spectral studies indicate coordination of tin to the oxygen, azomethine nitrogen and sulphur of the ligand moiety.     

Sensitive spectrophotometric determination of La(III) with 1-(2-pyridylazo)-2-naphthol

A simple and sensitive method for spectrophotometric determination of lanthanum has been developed. At pH 9.6, in presence of 50% ethanol, lanthanum reacts with 1-(-2-pyridylazo)-2-naphthol (PAN) to form a red complex which has two absorption maxima, at 545 and 510 nm. The molar absorptivity at 545 nm is 0.55 × 10⁴ liters · mol^?1 cm^?1. On the other hand, lanthanum reacts with PAN in pure ethanol to form a red complex at 530 nm, with high molar absorptivity (8 × 10⁴ liters · mol^?1 cm^?1).     

Co-nonsolvent systems for poly(ϵ-caprolactone) and poly(methyl methacrylate)

The cloud points for the co-nonsolvent systems (i) pyridine (PY) + formic acid (FA) towards poly(?-caprolactone) (PCL) or poly(methyl methacrylate) (PMMA) and (ii) pyridine + acetic acid (AA) towards PCL have been experimentally determined as a function of solvent composition at fixed polymer concentrations. Heats of mixing for the (FA + PY) system have also been measured. The single liquid approximation model correctly predicts for the (PY + FA) system the solvent composition at which the solvent power of the mixture is the poorest, provided it is recognized that the solvent system is comprised of pyridinium formate (PYFA) as one component and either PY or FA (depending on which is present in excess over 1:1 mole ratio) as the other. With the other co-nonsolvent system, the prediction is not as good. A possible reason for the discrepancy has been given.     

Dilute solution properties of sodium cellulose disulphate

Sodium cellulose sulphate (NaCaS), with degree of substitution (DS) of 1.90, was synthesized by reacting samples of cellulose, covering a wide range of average molecular weight, with S03/dimethyl formamide complex. A solution of NaCS in 0.5 M aq. NaCl was studied by solution viscometry, light scattering and membrane osmometry. The solution was dialysed against solvent. The following MarkHouwink-Sakurada equation and relation between the z-average radius of gyration and weightaverage molecular weight, Mw, were established for $\text{7.2 × 10}{}^4\text{?}\text{M}{}_{\mathrm{w}}\text{? 1.5 × 10}{}^6\text{at 25°}$.The NaCS with salt system was analysed according to the theory of linear non-ionic polymers. Flory's viscosity parameter φ is significantly molecular weight dependent. The partially free draining effect and the excluded volume effect were estimated and the former predominated. The unperturbed chain can be regarded as Gaussian and its dimension A was found to be 1.21 × 10^?8 cmand the conformation parameter a was 2.9.     

Dimorphism in triple orthovanadates MIILaTh (VO4)3 (MII = Sr or Pb)

Triple orthovanadates, SrLaTh(VO₄)₃ and PbLaTh(VO₄)₃ are found to be dimorphic, the crystalline form depending upon the firing temperature. The low-temperature form has zircon structure and the corresponding high-temperature form exhibits its well-known monoclinic modification. The X-ray powder diffractograms and infrared spectra are recorded and discussed in comparison with those of structurally related compounds.     

Thermally induced incomplete high-spin (5T2) ⇌ low-spin (1A1) transition in solid bis[2-(2-pyridylamino)-4-(2-pyridyl) thiazolato]iron (II)

The ⁵⁷Fe Mössbauer effect in two samples (A and B) of [Fe(papt)₂] and in its solvates with CHCl₃ and C₆H₆ has been studied between 4.2 and 343 K and clearly indicates a temperature induced high-spin (⁵T₂) ? low-spin (¹A₁) transition in these compounds [paptH = 2-(2-pyridylamino)-4-(2-pyridyl) thiazole]. At 343 K, sample B shows a doublet with ΔE_Q = 2.03 mm s^?1 and δIS = +0.87 mm s^?1, characteristic of a ⁵T₂ ground state. At 257 K, a second doublet, typical for a ¹A₁ ground state, is observed and its intensity increases as the transition progresses but levels off below ～ 100 K. At 4.2 K, 83% of the intensity is due to the ¹A₁ state, and ΔE_Q(¹A₁) = 1.56 mm s^?1 and δ^IS(¹A₁ = +0.32 mm s^?1. In an applied magnetic field, V_zz(¹A₁) < 0 and η ≈ 0.7 have been determined, whereas for the ^sT₂ ground state, V_zz(^sT₂) > 0, η ≈ 0.75, and an internal hyperfine field H_n ≈ ?13 kG have been observed. Similar results have been obtained with the other samples.Debye-Waller factors f5_T2 and f1_A1 were determined from the saturation corrected areas in the Mössbauer spectra, assuming Curie-Weiss dependence of the magnetic susceptibility for the ⁵T₂ and constant υ_cff for the ¹A₁ ground state. The temperature dependence of ?In f1_A1 closely follows the Debye model with Θ1_A1 = 165 K, whereas the same applies to ?ln f5_T2 only above ～ 210 K and Θ5_T2 = 134 K. The nature of the observed transition is discussed and the data presented are shown to be incompatible with a model based on a Boltzmann distribution between the two states.