Chemicals from Synthesis Gas : By Robert A. Sheldon (Series: Catalysis by Metal Complexes) D. Reidel Publishing Company,Dordrecht, The Netherlands, 1983, xx + 216 pages,Dfl. 110.00, US$ 48.00. ISBN 90-277-1489-4.

Photolysis of cis-HMn(CO)₄PPh₃ in the presence of H₂ and 1-alkene results in catalytic hydrogenation and isomerization of the alkene. The isomerization leads to cis- and trans-2-alkene in the presence or absence of H₂. Catalytic hydrogenation also occurs when cis-CH₃Mn(CO)₄PPh₃ is irradiated in the presence of H₂; use of D₂ leads exclusively to CH₃D. The possible mechanism of the hydrogenation is discussed.     

Metals in Biochemistry : P.M. Harrision and R.J. Hoare. Publ. Chapman & Hall,London and New York 1980, 78 pp + index. Price £2.45

The complex H₂Os₃(μ₃-NCH₃)(CO)₁₂ in decalin at 198°C in 35% yield. Crystal data for the former obtained at ?158°C are: orthorhombic, space group Pmcn, a 14.113(2), b 6.605(1), c 17.683(4) », Z = 4, D_c 3.44 g cm^?3. The hydrogen atoms are related by symmetry. The position of the unique hydrogen atom has been refined. It is observed asymmetrically bridging (closer to the unique Os atom) the longer edge of the isosceles triosmium triangle. The hydrogen atoms are out of the trimetal plane away from the triply-bridging nitrogen atom.Crystal data for the tetraosmium complex at 25°C are: monoclinic, space group C2/c a 30.818(9), b 8.463(2), c 16.621(2), », β 108.90(2)°, Z = 8, D_c 3.75 g cm^?3. The four osmium atoms form a distorted tetrahedral framework capped by the nitrogen atom of the methylnitrene group on the face containing the three longer OsOs separations.     

Internal dynamics of the LaI3 molecule. II. Thermal average structure of the molecule and mean square vibration amplitudes

The structural parameters of the effective r _g configuration of the LaI₃ molecule were calculated using the DFT/B3LYP method. The difference between the calculated values of r _e (La-I) and r _g (La-I) is mostly due to the anharmonicity of the ν₁ and ν₂ vibrations and does not exceed the error in determining the distance r _g (La-I) in the electron diffraction experiment. Inclusion of the anharmonicity of the ν₂ and ν₄ deformation vibrations in calculations leads to decreased amplitudes l(I…I) and shrinking effect δ(I…I) compared to the respective values obtained in the harmonic approximation. The LaI₃ molecule proved to be more rigid than predicted by B3LYP calculations.     

The unattainability of a unified E.M.F. series for molten salts the relation between the temperature coefficient of isothermal cells and the thermoelectric coefficients of thermocells

It is shown that the e.m.f. of a cell (T₁) A¦AX¦BX¦B (T₂) can not be split unambiguously into a combination of an isothermal cell A¦AX¦BX¦B either at T₁ or at T₂ and a thermocell either B¦BX¦B or A¦BX¦A between T₂ and T₁. The difference Δ in e.m.f. of both possible combinations is equal to FΔ/(T₂ - T₁) = ^*S(X^? in AX) - ^*S(X^? in BX).In examples given for molten silver and cuprous halides this difference in transported entropies is 1–2 cal mol^?1 K^?1 or Δ equal to 17.5–35 mV for T₂ - T₁ = 400 K. It is impossible to obtain unambiguously a unified e.m.f. series. The same qualitative conclusion is reached on the basis of the second law of thermodynamics from a discussion of an irreversible cyclic process involving the four cells mentioned.     

Etablissement du diagramme binaire hydroxy.2 naphtalene-chloro.2 naphtalene par differentes analyses thermiques

The phase diagram of the 2-chloronaphthalene-2-hydroxynaphthalene binary system has been established in three thermal investigations (calorimetric, crystallographic and optical methods). This diagram is fairly complicated. The main feature is the presence of three invariants: a eutectoid atT _e =309 K, a peritectic atT _p =333 K and a metatectic atT _m =364 K.     

Xanthone. I. optical detection of an extremely large sublevel splitting the lowest triplet state

The phosphorescence spectrum of xanthone in n-hexane is resolved into three components, one of which is due to thermally activated emission from a n_π* origin. The other two emissions originate from extremely widely split sublevels of the lowest triplet state, which is of ³ππ* origin. higher energy of T_Lx, and T_1y, and thus below 4K there is thermal depletion of T_1z which has the largest radiative strength. Th consequence of spin-orbit coupling between the T_x and T_y sublevels of the-two very close-lying, lowest triplet states. There are signif mixing of orbital character, a mixing which is governed by spin-orbit coupling rather than vibronic coupling.     

The use of CO2 gas as an in-situ dosimeter for d.c. and microwave pulse-radiolysis conductivity experiments

Carbon dioxide gas at a few hundred torr pressure is proposed as a convenient, in-situ dosimetric and test medium for d.c. and microwave pulse radiolysis conductivity experiments. The dose in gray is related to the (pressure independent) conductivity by D_g=2.89 × 10² σ_CO2 where σ_CO2 is the radiation induced conductivity in units of ω^-1m^-1. The measurement of σ_CO2 and the parameters required for extrapolation to other gaseous and condensed media are discussed. The time required for electron thermalization in CO₂ gas at atmospheric pressure is determined to be approximately 100 ps.     

3nπ* spectra of benzaldehyde. I. Vapor phosphorescence

Vibrational analysis of the vapor ³nπ* phosphorescence for three isotopic benzaldehydes (B-h₆, B-1d₁, B-Rd₅) shows that the out-of-plane aldehyde hydrogen wagging vibration (ν₂₆) is the most active non-totally symmetric mode in the spectrum. Since the intensity of 26₂⁰ ? 26₁⁰ the mechanism of ν₂₆ activity is primarily as a Franck—Condon mode. The only other out-of-plane mode definitely attributed to the vapor phosphorescence is the weakly active CHO torsional vibration (ν₃₆) with I (36₁⁰) > I (26₁⁰). Other Franck—Condon modes are ν₇, ν₂₅, ν₂₀, ν₁₇ and ν₈.     

Location of energy barriers. VII. Sudden and gradual late-energy-barriers

In the earlier papers of this series it was noted that barriers of “type II” (“Late barriers”, associated with substantially endothermic reaction) exhibited a large cross section if a given reagent energy was present predominantly as vibration in the bond under attack. It was found, however, that it was advantageous to retain in the reagents an amount of translation sufficient to surmount that part of the endothermic energy barrier which lay in the coordinate of approach; this could be identified with the repulsive part of the energy-release in the reverse, exothermic, reaction. In the present 3D classical trajectory study we compare S_r(V′)_T′+V′, for two endothermic surfaces with almost identical barrier heights and late barrier-crest locations, but differing fractions of the barrier in the coordinate of approach. For the surface IIS with a “sudden” rise to the barrier crest (implying substantial attractive energy-release in the reverse direction), S_r(V′_T′+V′ increased continually with V′, despite very low T′. By contrast surface IIG with “gradual” rise to the barrier crest (highly repulsive in the reverse direction), exhibited an S_r(V′_T′+V′ that passed through a maximum. Two further surfaces were investigated; surface IIHS resembling IIS but with a substantially higher barrier, and surface I, IIG with an intermediate barrier-location and hence a large fraction of the barrier along the coordinate of approach. The dynamics exhibited S-type (sudden) behaviour on IIHS, and G-type (gradual) behaviour on I, IIG. The presence of a significant fraction of the barrier on G-type surfaces along the endothermic coordinate of approach correlated with a more gradual curvature of the repulsive wall. This is likely to contribute to the greater availability of translation for barrier-crossing on G-type surfaces. Increased reagent rotation, R′, increased the reactive cross-section for endothermic reaction; the indications are that the mechanism by which rotation is effective involves vibration-rotation interaction.     

Determination of the liquidus curves of phase diagrams of condensed systems by measuring their E.M.F.

The accuracy of the determination of the liquidus curves of phase diagrams of condensed systems by e.m.f. measurements of suitable cells is discussed. The accuracy of the evaluation of the experimental data may be increased by considering the activity coefficients of electroactive components of the system in the corresponding equations using a suitable method of graphical correlation of the measured isothermal data. A further method of polythermal evaluation of experimental data has also been suggested. From the dependence of E_{r, cell} vs. x′_i at a given T and of E_{r, cell} vs. T at a given x′_i for one-phase and multi-phase conditions, twice as many corresponding x_{i, sat}?T_PC pairs may be obtained from a suitably chosen set of measurements.     

Magnetic and spectroscopic investigation of partially reduced vanadium pentoxides. II. β′-CuxV2O5

The magnetic, electron paramagentic resonance (EPR), infrared (ir), and optical properties of β′-Cu_xV₂O₅ have been measured and interpreted. Magentic susceptibility studies indicate that β′-Cu_xV₂O₅ undergoes a semiconductor → metal transition near x = 0.60. For x ? 0.40, the magnetic data interpreted in terms of a ligand-field model in which the octahedral ²T_2g term of V⁴⁺ is split by the combined perturbations of axial distortion and spin-oribt coupling, with the result that the ²T_2g term is split into a magnetic ground level, a weakly magentic intermediate level, and a magnetic highest level. The results of the magnetic analysis further support the transition to metallic behavior with increasing x. The EPR spectra are motionally narrowed by electronic hopping at low temperatures, and the g-tensor and linewidth data are in good agreement with the magnetic results. The ir spectra are independent of x and exhibit narrow bands at 1020 and 995 cm^?1, which are attributed to the stretching vibration of multiple VO bonds. The optical spectra consist of two main bands whose peak positions shift to higher frequencies with increasing x, implying that the V⁴⁺O bond distances decrease with increasing x. The results of this study are in excellent agreement with Goodenough's interpretation of β-M_xV₂O₅.     

Correlation of the prigogine-flory theory with isothermal compressibility data. I. Systems with quasi-spherical molecules

The isothermal compressibilities K_T for cyclohexane + benzene, cyclohexane + toluene and benzene + toluene systems at 25, 35, 45 and 60°C have been used to test the Prigogine-Flory theory using Van der Waals and Lennard-Jones energy potentials. Flory's energy parameter X ₁₂ was calculated for these systems at the four temperatures. From X ₁₂ for the equimolar mixture, the following excess functions were calculated: (?V^E/?_p)_T which is related to K _T ^E , the heat of mixing H ^E , and the excess volume V ^E . The theory and any of the two potentials give (?V^E/?_p)_T which fit the experimental data, but H ^E and V ^E , calculated using the same X ₁₂ parameter, depart appreciably from the experimental data even though they agree in sign and have the essential features of the excess functions. The departure is apparent in both magnitude (in particular for the cyclohexane + benzene, and cyclohexane + toluene systems) and in the temperature dependence. The conclusion is that the X ₁₂ parameter does not predict the thermodynamic properties of these systems and the Lennard-Jones potential, involving a more complicated expression, does not contribute any improvement over the Van der Waals potential.     

Exciton transitions in quasi-one-dimensional crystals. 9,10-dichloroanthracene

Polarized reflection spectra of the first singlet transition of the α-crystalline form of 9,10-dichloroanthracene are reported. Crystal faces (001), (011) and (010) were examined in spectral range 450 to 350 nm at two temperatures, 5 K and 300 K. Two systems of transitions were observed. The first system is assigned to neutral excitons. Spectral similarities with unsubstituted anthracene and arguments based on the one-dimensional stacking of molecules are used to construct a model of the exciten band structures. The M-polarized ππ* molecular transition gives rise to a four branch band with two allowed transitions. The 0-0_b (A_g → A_u) transition lies 50–100 cm^?1 above the bottom of the exciton band and the 0-0_c′ (A_g → B_u) transition lies at the top of the band. In the reflection spectrum the Davydov splitting c′b for transverse excitons is 210 cm^?1. The exciton band of the 00 molecular transition is not isolated but overlaps the two-particle manifold of the 0–1 vibronic transition. As a result of the 0–1_c′ transition is unexpectedly strong in the spectra of the (010) face. The second system is polarized along the stack-axis a and starts 2500 cm^?1 above the first system. It is tentatively assigned as |a(A_g → B_u) charge transfer exciton transition in agreement with earlier observations.     

Hydrocarbon chemistry : by G.A. Olah (C. Eaborn). J. Organomet. Chem., 334 (1987) C49-C50.

Sequential displacement of both N₂ ligands from cis-[Mo(N₂)₂(PMe₂Ph)₄] by CNMe occurs by a dissociative (I_d) mechanism (k₂/k₁～5,k₁ 0.020 min^?1 at 273 K) via the intermediate cis-[Mo(N₂)(CNMe)(PMe)₂Ph)₄] For t-BuNC substitution, the only detected intermediate appears to be [Mo(CNBu-t)(PMe₂Ph)₄] and no intermediate was detected in reactions of trans-[Mo(N₂)₂(Ph₂PCH₂CH₂PPh₂)₂] with CNMe. N₂ appears to be labilised by cis-ligands in the order t-BuNC > CNMe > N₂ > NCR.     

The Fokker-Planck-Langevin model for rotational brownian motion. IV. Asymmetric top molecules

The general series expansion for the joint angular velocity-orientation conditional probability density for a fluid composed of asymmetric top molecules is derived, and expressions for the reorientational correlation functions, correlation times, spectral densities, and the correlation times relevant to magnetic relaxation via spin-rotation interactions are presented. The reorientational correlation times and spin-rotation functions computed using this Fokker-Planck-Langevin (FPL) model with isotropic friction tensor (τ_x = τ_y = τ_z) are compared with the corresponding times and functions computed with the J-diffusion limit of the extended diffusion (EDJ) model. The models are found to predict significantly different behaviour only in the regime where free rotation and precessional effects become important. The reorientation self- and cross-correlation times are shown to follow Hubbard relations in the limit of short τ_x, τ_y, τ_z. Numerical calculations of the FPL reorientational correlation functions, correlation times and spin-rotation functions show that these properties are sensitive to the anisotropies in the friction tensor in the rotational Langevin equation.     

Reduction of the titanium niobium oxides. II. TiNb24O62

Interpretation of the reduction path of TiNb₂₄O₆₂ is complicated by uncertainty about both the stoichiometric ranges of the possible block structures and the formation of TiNb solid solutions. Reduction forms the Me₁₂O₂₉ phase, probably from the outset, with an initial composition close to Ti₂Nb₁₀O₂₉, thereby rapidly depleting the Me₂₅O₆₂ phase of titanium. When log p_O2 (atm) has dropped to ?9.62, a phase approximately Ti_0.95Nb_11.05O₂₉ is in equilibrium with titanium-free Nb₂₅O₆₂ at its lower composition limit (NbO_2.471). Nb₂₅O₆₂ is then reduced to Nb₄₇O₁₁₆ without change in the Me₁₂O₂₉. At ?9.62>log p_O2 (atm) > ?10.0, niobium is transferred to the Me₁₂O₂₉ phase and Nb₄₇O₁₁₆ is consumed. A second univariant equilibrium is set up as Nb₄₇O₁₁₆ is reduced to Nb₂₂O₅₄. This is consumed in turn, to increase the niobium content of the Me₁₂O₂₉ until, at log p_O2 close to ?10.8, monophasic Ti_0.48Nb_11.52O₂₉ is formed. The (Ti,Nb)O₂ solid solution then appears and the final product is Ti_0.04Nb_0.96O₂, with the rutile superstructure cell reported for NbO₂.     

Thermolabile kohlenwasserstoffe. XXVI. Bildungsenthalpie von 1,1,2,2-tetra-tert-butylethan

The title compound (1) was prepared in high purity by reducing 3,3-dibromo-2,2,4,4-tetra-methylpentane (2) with magnesium in the last step. The heat of combustion, ΔH⁰_c(c), of 1 was measured using an aneroid isoperibol microcalorimeter and the heat of sublimation, ΔH_sub, was obtained from the vapour pressure (35–93°C) measured in a flow system. The results: ΔH⁰_c(c) = ?2913.3(±0.9), ΔH⁰_f(c) = ?77.6(±0.9) and ΔH⁰_f(g) = ?59.9(±0.9) kcal mol^?1 lead to an outstandingly high value for the excess strain enthalpy (H_s = 66.3 kcal mol^?1) revealing strong van der Waals repulsions in this highly crowded alkane.     

iR correction: Part II. Effect on corrosion monitoring

The effect of iR drop on the corrosion rates obtained by curve fitting of the polarisation data around the corrosion potential is an increase in the corrosion current calculated, which is in direct contrast to linear polarisation measurements. The b_a values and, for an activation-controlled cathodic process the b_c values, are increased by added ohmic resistance, R_u. This more than offsets the increase in R_p and so the i_corr increases. For a diffusion-controlled cathodic process the b_c becomes negative with added R_u. All the results are not unduly affected by up to ±2% random error. A current-interrupt method of iR correction has been used for steel corroding in a deaerated H₂SO₄ solution to demonstrate the effect of iR correction.