Rate parameters for transfer reactions of some polymer radicals: in terms of Swain and Lupton's f and r and the unique positional weighting factors of Williams and Norrington

Rate parameters of the reaction of phenols, deuterated phenols and nitrobenzenes with polyvinylacetate radicals and of aromatic thiols with polymethylmethacrylate radicals have been correlated with Swain and Lupton's substituent constants (F_k and R_k) and Williams and Norrington's unique positional weighting factors (f_j and r_j) by the following equation: $\text{P}{}_{\mathrm{i}}\text{= α}{}_{\mathrm{i}}\text{?}{}_{\mathrm{j}}\text{F}{}_{\mathrm{k}}\text{+ β}{}_{\mathrm{i}}\text{r}{}_{\mathrm{j}}\text{R}{}_{\mathrm{k}}\text{+ e}{}_{\mathrm{i}}\text{+ P}{}^0{}_{\mathrm{i}}$where P_i's are the rate parameters, P⁰_i being that for a standard reference state. The correlations were found to be quite satisfactory. The sign and magnitude, and the ratio of the reaction dependent parameters α_i and β_i throw light on the nature of the transition state and the relative contributions of the mesomeric and inductive effects. The present studies also show that the mesomeric effect of meta-substituents is significantly greater than reported by earlier workers.     

Investigations on the influence of charge density on the mutual deactivation of polyion-macroradicals—II

Bimolecular rate constants (2 k_R) of the reaction R· + R· in aqueous solution were measured using the pulse radiolysis technique. R· designates radicals produced by H atom abstraction from polyvinyl alcohol partially acetalyzed with glyoxylic acid. Due to the expansion of the coils, 2 k_R increases with X_i the content of ionized base units in mole %. Above a critical value x_i (crit), 2 k_R decreases due to intermolecular repulsion. x_i(crit) decreases with increasing chain length $\text{n}{}_{\mathrm{<mtext>n</mtext>}}$ [x_i (crit) ≈ 0·5 mole % at $\text{n}{}_{\mathrm{<mtext>n</mtext>}}\text{= 3000}$ and x_i (crit) ≈ 1·5 mole % at $\text{n}{}_{\mathrm{n}}\text{= 270}$]. In the presence of NaClO₄, the following salt effects were observed: for x_i >x_i (crit), 2 k_R is increased because the intermolecular repulsion is partially depressed by screening. Below x_i (crit), 2 k_R is decreased since the coil expansion is diminished. At very low values of x_i where the coil expansion due to intramolecular repulsion is negligible, no salt effect was detectable.     

Nonstoichiometry and defect structure of the perovskite-type oxides La1−xSrxFeO3−°

In order to elucidate the defect structure of the perovskite-type oxide solid solution La_1?xSr_xFeO_3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, P_O2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of P_O2 ≥ 0.13 atm, δ in La_1?xSr_xFeO_3?δ was found to be close to 0. With decreasing log P_O2, δ increased and asymptotically reached $\text{x}\text{2}$. The value corresponding to $\text{δ =}\text{x}\text{2}$ was about ?10 at 1000°C. With further decrease in log P_O2, δ slightly increased. For LaFeO_3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log P_O2 is interpreted on the basis of the defect equilibrium among Sr′_La (or V?_La for the case of LaFeO_3?δ), V^··_O, Fe′_Fe, and Fe^·_Fe. Calculations were made for the equilibrium constants K_ox of the reaction

$\text{1}\text{2}\text{O}{}_2\text{(g) + V}{}^{\mathrm{··}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= O}{}^{\mathrm{x}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe}}$

and K_i for the reaction

$\text{2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= Fe}{}^{\mathrm{\prime }}{}_{\mathrm{Fe}}\text{+ Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe·}}$

Using these constants, the defect concentrations were calculated as functions of P_O2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.     

Low-temperature luminescence of Eu3+ in K2EuCl5

The luminescence associated with the Eu³⁺ ion in K₂EuCl₅ has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the ⁵D₀ and ⁵D₁ excited states, and transitions to the ${}^7\text{F}{}_0\text{,}{}^7\text{F}{}_1\text{,}{}^7\text{F}{}_2\text{,}{}^7\text{F}{}_3$, and ⁷F₄ ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective C₄ site symmetry for the emitting Eu(III) species, even though the crystal structure does not indicate the presence of a true or pseudo C₄ axis.     

Synthèse et caractéristiques cristallographiques des phases solides de type fluorine des systèmes PbF2LnF3

A preliminary study of the PbF₂LnF₃ systems (Ln = lanthanides and Y) has allowed the characterisation of three phases: a disordered fluorite-like solid solution Pb_1?xLn_xF_2+x the domain of which increases with increasing temperature and dopant ion radius, and two anion-excess fluorite related superstructures: Pb₂YF₇ (tetragonal, space group I4 or $\text{I4}\text{m}\text{, a \#}\text{a}{}_{\mathrm{<mtext>F</mtext>}}\text{√2}\text{, c \# 3a}{}_{\mathrm{<mtext>F</mtext>}}$) and Pb₄Ln₃F₁₇ with Ln = SmLu (rhombohedral, space group $\text{R3, a}{}_{\mathrm{<mtext>h</mtext>}}\text{\# (}\text{a}{}_{\mathrm{<mtext>F</mtext>}}\text{√2}\text{)√7, c}{}_{\mathrm{<mtext>h</mtext>}}\text{\# 2a}{}_{\mathrm{<mtext>F</mtext>}}\text{√3}$). The crystallographic characteristics of the two ordered phases have been confirmed by electron diffraction.     

Primary radical termination in polymerization: Evaluation of the characteristic constant

Polymerization experiments with styrene in benzene at 60°, initiated by benzoyl peroxide, covering a wide range of concentration of both monomer and initiator are reported; the results cannot be explained in terms of the classical rate relationship with $\text{R}{}_{\mathrm{p}}\text{∝ [}\text{I}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{M}\text{]}$. Deviations were reflected in unexpected orders of monomer up to [M]^1·4 and of initiator down to [I]^0·42 when the initiator concentration is increased and monomer concentration is decreased. Based on the concept of primary radical termination, an equation, viz.

$\text{ln}\text{R}\text{p}\text{2}\text{[I][M]}{}^2\text{=}\text{ln}\text{2f}{}_{\mathrm{k}}\text{k}{}_{\mathrm{d}}\text{k}\text{p}\text{2}\text{k}{}_{\mathrm{t}}\text{?2}\text{k}{}_{\mathrm{prt}}\text{k}{}_{\mathrm{i}}\text{k}{}_{\mathrm{p}}\text{×}\text{R}{}_{\mathrm{p}}\text{[M]}{}^2$

is proposed. Semi-log plots of R_p²/[I] [M]² vs R_p/[M]² show a wide range of linearity; the characteristic constant k_prt/k_ik_p and also f_k can be obtained from the slope and intercept, respectively, k_prt, k_i and k_p are, respectively, the rate constants of primary radical termination, initiation and propagation and f_k is the efficiency of initiation, defined as the fraction of radicals which come out of the solvent cage and take part in initiation, primary radical termination and primary radical recombination. The definition of f_k is thus differentiated from the conventional efficiency of initiation. Finally, we have derived an equation which allows determination of the classical efficiency of initiation as a function of [I]/[M]² and also allows a correction of R_p in handling the above equation by taking into account the small amount of monomer consumed in initiation.     

Linear expansion of the eigenvalues of a Hermitian matrix and its application to the analysis of the electronic spectra of 3d ions in crystals

It is shown that the eigenvalues E_i of a Hermitian matrix H with matrix elements H_ij = Σ_kA^k_ija_k, where A^k_ij are known numbers and a_k a set of parameters, can be exactly expanded as $\text{E}{}_{\mathrm{i}}\text{= Σ}{}_{\mathrm{k}}\text{(}\text{?E}{}_{\mathrm{i}}\text{?a}{}_{\mathrm{k}}\text{)a}{}_{\mathrm{k}}$. This property is applied to the analysis of the optical spectra of transition metal ions in crystals proposed by L. Pueyo, M. Bermejo, and J. W. Richardson (J. Solid State Chem.31, 217, 1980), and it is shown that this method represents the best fit of the Hamiltonian eigenvalues to the observed (or calculated) spectrum. Further advantages of using this property, in connection with the spectral analysis, are the minimization of the errors associated with the numerical approximations and a reduction in computer time. In the molecular orbital calculation of the optical or uv spectra of these systems, this linear expansion of the eigenvalues give a detailed interpretation of the improvements produced by refined calculations, such as those including configuration interaction. In particular, the changes in one-electron energy and in open-shell repulsion interactions associated with the refinement can be clearly and easily formulated. As examples, the computed spectra of CrF^4?₆ and CrF^3?₆ are discussed.     

Isotope effects in electron-donor-acceptor complexes involving aromatic hydrocarbons and fluoranil from NMR shift measurements

Equilibrium constants and NMR shift parameters have been determined for complexes of benzene, toluene and p-xylene and their perdeutero-analogues with fluoranil in cyclohexane solution from NMR shift measurements. Isotope effects are observed in the 1:1 equilibrium constants for the complexes of p-xylene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$= 1.1₀) and toluene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$ = 1.0₉). A much smaller effect was observed for the benzene complex which could not be quantified. These results may be interpreted through either the larger electronegativity of H over D, or the greater steric requirements of H over D.     

General approach to polymer properties dependent on molecular characteristics

The general equation

where P is a polymer property, Π is the sign of product, A is a constant, v_i is the ith variable and a_i is the exponent of ith variable, has been proposed for the dependence of some polymer properties on molecular weight, molecular weight distribution and long-chain branching. The data confirming the proposed equation have been taken from published theoretical and experimental papers on intrinsic viscosity, melt viscosity and glass transition temperature, as well as on viscosity of polymer solutions. Examples of application are given.     

Cryogenic luminescence studies of Eu3+ in LiEuCl4

The luminescence associated with the Eu³⁺ ion in LiEuCl₄ has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the ⁵D₀ and ⁵D₁ excited states, and transitions to the ${}^7\text{F}{}_0\text{,}{}^7\text{F}{}_1\text{,}{}^7\text{F}{}_2\text{,}{}^7\text{F}{}_3$, and ⁷F₄ ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective D₄ site symmetry for the emitting Eu³⁺ species, even though the europium polyhedron was found to be that of a bisdisphenoid.     

Etude comparative des structures type K4NiF4 et pérovskite par la méthode des invariants

The study of K₂NiF₄ and perovskite structure type by the “method of invariants” leads to the relationship: $\text{(A-X)}{}_9\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? (A-X)}{}_{12}\text{=}\text{constant}$, where (A-X)₉ and (A-X)₁₂ are the invariant values associated with cation A in coordination number 9 and 12. In the case where A = K⁺ and X = F^?, we propose the relationship:

$\text{(K}{}^{\mathrm{+}}\text{?F)}{}_{\mathrm{R}}\text{= 2.832 R}{}^{\mathrm{<mtext>1</mtext><mtext>11.4</mtext>}}$

where R is the coordination number.     

KxP2W2O16: A bronze with a tunnel structure built up from PO4 tetrahedra and WO6 octahedra

The structure of a $\text{K}{}_{\mathrm{x}}\text{P}{}_2\text{W}{}_4\text{O}{}_{16}\text{(x ? 0.4)}$ crystal was established by X-ray analysis. The solution in the cell of symmetry $\text{P2}{}_1\text{m}$, with a = 6.6702(5), b = 5.3228(8), c = 8.9091(8) Å, β = 100.546(7)°, Z = 1, has led to R = 0.033 and R_w = 0.036 for 2155 reflections with $\text{σ(I)}\text{I}\text{≤ 0.333}$. This structure can be described as two octahedra-wide ReO₃-type slabs connected through “planes” of PO₄ tetrahedra. A new structural family K_xP₂W_2nO_6n+4 can be foreseen which is closely related to the orthorhombic P₄W₈O₃₂ and the monoclinic Rb_xP₈W_8nO_24n+16 series.     

Excess volumes and isentropic compressibilities for (2-ethoxyethanol + n-heptane) at 298.15 K

Excess volumes and ultrasonic speeds have been measured for (2-ethoxyethanol + n-heptane) at 298.15 K. Isentropic compressibilities, excess isentropic compressibilities, and the partial molar excess quantities $\text{K}{}_{\mathrm{<mtext>S,\; </mtext><mtext>i</mtext>}}{}^{\mathrm{<mtext>E</mtext>}}\text{= ?(}\text{?V}{}_{\mathrm{i}}{}^{\mathrm{E}}\text{?p}\text{)}{}_{\mathrm{S}}$ were calculated from the results. The excess volume is positive over the entire mole-fraction range, whereas the curves for the excess isentropic compressibility is sigmoid with negative values occurring at mole fractions of 2-ethoxyethanol greater than 0.35. A qualitatitive interpretation of the results is presented.     

Kinetics and mechanism of the interaction of hexaaquochromium(III) with octacyanomolybdate(IV) ions

The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H⁺ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H₃O⁺]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE^* = 1.3 × 10² kJ mol^?1, ΔH^* = 129 kJ mol^?1, ΔS^* = ?315 e.u., ΔF^* = 2.3 × 10² kJ and A = 1.5 × 10^?3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: k_obs=$\text{[}{}_{\mathrm{kK}}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k′K′k}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k}{}_{\mathrm{<mtext>h</mtext>}}\text{+[}\text{K}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{K′}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}$     

Termination and transfer of the polymer chain to a maleimide derivative containing the azo group

The copolymerizations of N-(3-dimethylaminophenyl) maleimide (I) and 4-(2-chlorophenyl)azo-3-maleimido-N,N-dimethylaniline (II) with styrene were investigated; the copolymerization parameters of the pairs ($\text{I}\text{+}\text{styrene}$) and ($\text{II}\text{+}\text{styrene}$) and $\text{k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ hr I at 50° were determined; chain transfer to the maleimide ring of I was proved. The homopolymerization of styrene in the presence of 4-(2-chlorophenyl)azo-succinimide-N,N-dimethylaniline (III) was used to determine the ratio of the rate constant for addition of the polystyrene radical to the azo group in III to k_p for styrene.     

Thermodynamic properties of two metal-rich tantalum sulfides: Ta2S and Ta6S

The incongruent vaporization reactions of Ta₂S and Ta₆S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of P_S(obs) to equilibrium the enthalpies of the reactions $\text{3}\text{2}\text{Ta}{}_2\text{S(s)}\text{=}\text{1}\text{2}\text{Ta}{}_6\text{S(s) + S(g)}$ and Ta₆S = 6 Ta(s) + S(g) were found to be $\text{ΔH}{}^0{}_{298}\text{R}\text{= 53.0(0.3) · 10}{}^3\text{K}$ and $\text{ΔH}{}^0{}_{298}\text{R}\text{= 58.1(0.4) · 10}{}^3\text{K}$, respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation.     

Molecular structure of 1,1-dichloroethylene as studied by gas electron diffraction and microwave data. Estimation of equilibrium structure by an extended anharmonic model analysis

The r_z structure of 1,1-dichloroethylene has been determined by a joint analysis of the electron diffraction intensity and the rotational constants as follows: $\text{r}{}_{\mathrm{<mtext>z</mtext>}}\text{(}\text{CH}\text{) = 1.088 ± 0.011, r}{}_{\mathrm{<mtext>z</mtext>}}\text{(}\text{CC}\text{) = 1.329 ± 0.003, r}{}_{\mathrm{<mtext>z</mtext>}}\text{(}\text{CCl}\text{) = 1.725 ± 0.002}\text{A}\text{?}\text{, ∠}{}_{\mathrm{<mtext>z</mtext>}}\text{HCH}\text{= 121.4 ± 0.7}\text{and}\text{∠}{}_{\mathrm{<mtext>z</mtext>}}\text{ClCCl}\text{= 114.1 ± 0.2°}$. The uncertainties represent estimated limits of error. The observed structural parameters are compared with those for related compounds and the systematic trends in the bond lengths and bond angles are discussed. The effective constants representing anharmonicity have been obtained from an analysis of the isotopic differences in the r_z structure. By using the r_z parameters and the effective constants, the equilibrium structure has been estimated as follows: $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{CH}\text{) = 1.079 ± 0.012, r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{CC}\text{) = 1.324 ± 0.005, r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{CCl}\text{) = 1.721 ± 0.003}\text{A}\text{?}\text{, ∠}{}_{\mathrm{<mtext>e</mtext>}}\text{HCH}\text{= 120.5 ± 0.8}\text{and}\text{∠}{}_{\mathrm{<mtext>e</mtext>}}\text{ClCCl}\text{= 114.0 ± 0.3°}$.     

Oligomerisation anionique de l'ethylene—VI. Amorcage par le nBuLi complexe par diverses polyamines bitertiaires

In the field of anionic initiators of ethylene oligomerization, we have studied the reactivity of nBuLi complexed by tertiary amines such as tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA) and pentamethyldiethylenetriamine (PMDT). RMN shows high field shift of the —CH₂— protons next to the lithium. This shift is less important for TEEDA compared to those for TMEDA and PMDT. Steric hindrance due to the ethyl groups of TEEDA seems to forbid easy access of the nitrogen atoms to the lithium counter-ion. These results agree well with the kinetic studies which indicate the absence of aggregated species. The following equations have been established: $\text{V}{}_{\mathrm{p}}\text{= k}{}_{\mathrm{p}}\text{·K}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{D}}\text{[(}\text{nBuLi:TMEDA}\text{)}{}_2\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{Et}\text{]}$. and V_p = k′_p[nBuLi:TEEDA][Et]