The effect of pH on some outer-sphere electrode reactions at carbon electrodes

The apparent heterogeneous rate constant, k°_app, for three couples known to undergo outer-sphere electron transfer reactions has been investigated at carbon, gold, and platinum electrodes as a function of solution pH. The rates are found to be pH dependent at two different types of glassy carbon and at carbon paste but not at metallic electrodes. The rate is found to decrease with increasing pH for Fe(CN)^{$\text{3?}\text{4?}$}₆ and IrCl^{$\text{2?}\text{3?}$}₆, and the opposite effect is observed for the Ru(NH₃)^{$\text{3+}\text{2+}$}₆ couple. For the three compounds examined, the magnitude of the pH dependent rate changes can be associated with a change in the magnitude of the potential of the reaction layer induced by a change in surface charge of ～ 2 × 10^?7 C cm^?2. The pH dependence of the observed rate constant at glassy carbon can be attenuated by heat treatment, chemical reduction, or esterification of the surface. This behaviour is consistent with the theory that the pH dependence of k°_app arises from the presence of functional groups on the carbon surface.     

Cross-conjugated biradicals: Kinetics and kinetic isotope effects in the thermal isomerizations of cis- and trans-2,3-dimethylemethylnecyclopropane,cis- and trans-3,4-dimethyl-1,2-dimethylenecyclobutane,and of 1,2,8,9-decatetraene

cis- and trans - 2,3 - Dimethylenemethylenecyclopropane ($\text{C}$ and $\text{T}$) interconvert at 160.0° with a small normal kinetic isotope effect (KIE) when the exo-methylene is deuterated, but the 1,3-shift products, 2-methylethylidenecyclopropane, show a large normal KIE, 1.35 and 1.31, when formed from $\text{C}$ and $\text{T}$, respectively. This data can be interpreted in terms of either parallel reactions or a common trimethylenemethane diradical intermediate formed with a normal KIE of 1.11 and closing to 1,3-shift product with a normal KIE of 1.29 due to the effect of deuterium in the required 90° rotation of the exo-methylene carbon.The kinetics of the thermal 1,3- and 3,3-shifts of cis- and rans-3,4-dimethyl-1,2-dimethylenecyclobutane ($\text{CB}$ and $\text{TB}$) were determined in a flow reactor. The first order rate constants are log k_CB (sec^?1) = 13.7 ? 42,200/2.3 RT and log k_TB (sec^?1) = 13.6 ? 41,900/2.3 RT (E_a in kcal/m) which compare favorably to that from the parent hydrocarbon. 1,2-dimethylenecyclobutane, after reasonable correction for dimethyl substitution.Rearrangement of $\text{TB}$ and its bis(dideuteriomethylene) derivative at 230.0° revealed a normal KIE of 1.08. This KIE could be interpreted in terms of either a methylene rotational isotope effect in a concerted reaction or formation of a bisallyl diradical with the expected normal rotational IE on closure to the 1,3-shift product of 1.12 with no IE in the ring opening when the result is corrected for return of the biradical to starting material.The kinetics of intramolecular 2 + 2 cycloaddition of 1,2,8,9-decatetraene were determined in a flow reactor. The first order rate constant is log k(sec^?1) = 9.4 ? 30,800/2.3 RT (E_a in kcal/m). These energetics are compared with those of other 2 + 2 cycloadditions. The major product is 3,4-dimethylenecyclooctene ($\text{DC}$) which is also found from the minor product, cis-7,8-dimethylenebicvyclo[4.2.0]octane ($\text{CO}$), at higher temperatures. The trans isomer, $\text{TO}$, also gives $\text{DC}$ at about the same rate as $\text{CO}$.     

Electric moments,polarizabilities and hyperpolarizabilities for BH(X1Σ+ and CH+ (X1Σ+)

The electric moments and static polarizabilities of BH(1σ²2σ²3σ², X¹Σ⁺) and CH⁺ (1σ²2σ²3σ², X¹Σ⁺) were calculated at the experimental internuclear separation in the LCAO SCF MO approximation. Most of the molecular properties reported in this paper for BH and CH⁺ appear for the first time and should be close to the Hartree—Fock limit. All tensors up to the fourth rank have been included in this study. The isotropy and anisotropy of the α, β and γ tensors are, in atomic units. $\text{α}$ = 22.71, Δα = ?0.26, $\text{β}$ = 55.1, Δβ = ?183.7, $\text{γ}$ = 12428, Δ₁γ = 37895, Δ₂γ = 25120 for BH and $\text{α}$ = 7.73, Δα = 0.39, $\text{β}$ = ?12.4, Δβ = ?11.7, $\text{γ}$ = 344, Δ₁γ = 1515, Δ₂γ = 750 for CH⁺.     

Observation of new bands in the N2 Herman infrared system and kinetic study of its formation in a pulsed-discharge apparatus

Four new bands of the unassigned N₂ Herman infrared system (HIR) are observed in a pulsed-discharge apparatus. The upper HIR state is produced by the N₂(A) + N₂(A) energy pooling reaction which is studied by time-resolved spectroscopy; its production rate constant is found to be ?4 × 10^?11 cm³ molecule^?1 s^?1 and its energy $\text{}\text{?}$12eV.     

Observation of nonlinearity and asymmetry in energies of EPR transitions of 160Gd3+ in La(C2H5SO4)3 · 9D2O at low magnetic fields

The energies of EPR transitions of ¹⁶⁰Gd³⁺ in La(C₂H₅SO₄₃ · 9D₂O at 77.2 K are observed to be nonlinear functions of field at low fields. The + $\text{3}\text{2}$, + $\text{1}\text{2}$ and ?$\text{3}\text{2}$, ?$\text{1}\text{2}$ transition energies converge asymmetrically below 10 G and differ by only ≈ MHz at the lowest fields employed.     

Emission spectra of supersonically cooled chloroacetylene cations

The ā²Π_Ω → X?²Π_Ω, Ω = $\text{3}\text{2}$, $\text{1}\text{2}$ emission spectra of rotationally cooled chloro- and deuterochloro-acetylene cations have been obtained by electron-impact ionisation of a seeded helium supersonic free jet. The resultant spectral improvements lead to the identification of the spin-orbit components and isotope splittings and to a vibrational assignment of the prominent bands. The vibrational frequencies could be determined to within ±1 cm^?1 for many of the fundamentals for the cations in the X?²Π_Ω and ā²Π_Ω electronic states.     

Temperature dependence of collisional deactivation of Tl(62P32)

The rate coefficients for the collisional deactivation of Tl(6²P_{$\text{3}\text{2}$}) by several gases has been determined at 300°K. This data is compared with that previously obtained at higher temperatures and the Arrhenius parameters calculated. Both the overall rate coefficients and temperature effects display trends similar to those observed for 1(5²P_{$\text{1}\text{2}$}) relaxation. The deactivation of Tl(6²P_{$\text{3}\text{2}$}) by O₂ is shown to proceed by a process involving an equilibrium with Tl(6²P_{$\text{1}\text{2}$}) and electronically excited oxygen, probably O₂(¹Δ_g).     

The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring disk electrode techniques: III. Cathodic reduction of chromium(0) π-complexes and the corresponding arenes in dimethyl sulfoxide solutions

The rotating disk (RDE) and the rotating ring-disk (RRDE) electrode techniques have been employed to study the cathodic behavior of eight bisarenechromium complexes and seven corresponding arenes in DMSO solutions. In the first electrochemical step of the process reversible addition of one electron results in anion-radicals, whose formation has been demonstrated for certain arenes and chromium π-complexes by oxidation of these particles on the ring electrode.Substituents on different ligands of bisarenechromium complexes were found to exert pronounced mutual influences. The role of the chromium atom in transfer of electronic effects from one ligand to another is discussed.It was found that a linear correlation exists between the variations in the free energy of the equilibrium “initial compound

anion-radical” (due to coordination of free arene with chromium which is displayed as a shift of the cathodic process half-wave potential ΔE_{$\text{1}\text{2}$}^CL) and the half-wave potential of the oxidation of the corresponding Cr⁰ π-complex to a cation E_{$\text{1}\text{2}$}^X ΔE_{$\text{1}\text{2}$}^CL = a + αE_{$\text{1}\text{2}$}^X At E_{$\text{1}\text{2}$}^X < ?0.3 V, complex formation slows down the cathodic process and at E_{$\text{1}\text{2}$}^X > ?0.3 V the process is facilitated.     

Zur konformation und intramolekularen beweglichkeit von [6]paracyclophan-8,9-dicarbonsäurediethylester)

The title compound 1 prepers the conformations $\text{1a}$/$\text{1b}$ predicted for [6]paracyclophane; the barrier for the intramolecular process $\text{la}$ ? $\text{1b}$ was found to be Δ G⁺ = 13.9 kcal/mol at +4°C.     

Conformational behaviour and inclusion compound forming properties of 5,18-disubstituted derivatives of 5, 11, 12, 18-tetrahydrotribenzo[b,f,j][1,4]diazacyclododecine-6, 17-dione

An X-ray structure analysis shows that the 5, 18-dimethyl derivative ($\text{5}$) of the title compound ($\text{4}$) crystallises from xylene as a 1:1 inclusion compound in which the host molecules adopt propeller-like conformations ($\text{7}$ and $\text{7}$*) with almost perfect $\text{C}$₂ symmetry. Dynamic ¹H n.m.r. spectroscopy shows that the 5, 18-dibenzyl derivative ($\text{6}$) of ($\text{4}$) forms a 1:1 inclusion compound with ethanol in the solid state and undergoes ring inversion ($\text{7}$ ? $\text{7}$*) between enantiomeric propeller-like conformations in solution against a barrier of 21.1 kcal mol^?1     

Extraction of indium(III) from chloride medium with 1-phenyl-3-methyl-4-acylpyrazol-5-ones. Synergic effect with high molecular weight ammonium salts.

The extraction of In(III) from 1M (Na,H)(Cl,ClO₄) media with 4-acylpyrazol-5-ones (HL) in toluene at 25°C is described by equilibria In ³⁺ + 3 $\text{HL}$ ? $\text{InL}{}_3$ + 3 H⁺ (log K = 1.48, 1.03, 0.87 with acyl = benzoyl, lauroyl, 2-thenoyl), InCl ²⁺ + 2 $\text{HL}$ ? $\text{InClL}{}_2$ + 2 H⁺ (log K = 0.26, ?0.45, ?0.35 respectively) and In³⁺ + m Cl^? ? InCl_m^(3-m)+ (log β_m available from literature). The extraction from 1M (Na,H)(Cl,NO₃) medium is enhanced by addition of aliquat (TOMA⁺,Cl^?) and the following synergic equilibrium takes place : $\text{InCl}{}_2$ + $\text{(TOMA}{}^{\mathrm{+}}$,Cl^?) ? $\text{(TOMA}{}^{\mathrm{+}}$, InCl₂L₂^? (log K = 5.49, 5.25, 5.21 respectively). Cl^? of (TOMA⁺,Cl^?) is exchanged by NO₃^? with the equilibrium constant log K = 1.50. If (TOMA⁺,Cl^?) is replaced by tri-n-octylammonium chloride, the synergic effect is largely reduced (log K = 4.17 with acyl = benzoyl). The extraction from chloride solutions containing ClO₄^? remains unchanged by addition of ammonium salts.     

Quenching of the Ba + Cl2 chemiluminescence: Estimate of BaCl*2 radiative lifetime

The chemiluminescence produced by the Ba + Cl₂ reaction was recorded as a function of He and N₂ pressure. A modified Stern-Volmer treatment of competitive electronic quenching of BaCl^* and BaCl^*₂ emission yielded upper limits to the half pressures p_{$\text{1}\text{2}$}(He) ? 9.0 ± 3 mtorr and p_{$\text{1}\text{2}$} (N₂) ? 1.1 ± 0.2 mtorr for quenching of BaCl^*₂ by helium and nitrogen, respectively. A lower limit of the BaCl^*₂ radiative lifetime is placed at τ_R ? 100 μ.     

Anomaly in dispersion intermolecular potential produced by intense radation field

It is predicted that a gap of 2μE/3^{$\text{1}\text{2}$} appears in the dispersion potential for a pair of ground-state (identical) atoms, or molecules, at distance R such that ?δ + (4π?₀)^?1($\text{μ}{}^2\text{3}\text{R}{}^3$)(1 ? 3 cos²θ) = 0, where μ is the electric dipole moment, E is the field strength of an intense radiation field and θ is the angle between the polarization direction of the field and R. The detuning term Δ is ω₀?ω where ω₀ is the transition frequency of the atom or molecule, and ω is that of the field. The gap is of the order of 10¹¹ Hz when the intensity of the radiation field is a few $\text{MW}\text{cm}{}^2$.     

The thiolate anion as a nucleophile Part XI. Effect of the size of the nucleophile

The nucleophilic substitution reactions of some simple fluorobenzenes, C₆H_6?xF_x with sodium methanethiolates Na⁺SR^?(R=Et, $\text{i}$-Pr, $\text{t}$-Bu) have been studied. Some fully substituted products, C₆H_6?x(SR)_x, could be obtained in DMF as solvent with R = Et and $\text{i}$-Pr, but not when R = $\text{t}$-Bu. All the new products isolated have been characterized by elemental analysis, and NMR (H-1 and F-19), infrared and mass spectroscopy.     

Étude quantitative d'équilibres chimiques en solution dans les sels fondus par spectrophotométrie d'absorption: Application au neptunium

The following reactions: NpO₂⁺+4 HCl ? Np⁴⁺ + 2 H₂O + $\text{1}\text{2}$ Cl₂ + 3Cl^- NpO₂⁺+$\text{1}\text{2}$ Cl₂ ? NpO₂²⁺ +Cl^- 2HCl+O^2- ? H₂O +Cl^- have been examined quantitatively. The reactions were studied in fused LiCl-KCl sparged with gas mixtures of definite compositions. The concentrations of the diffrent neptunium species were measured by absorption spectrophotometry. The values of respective equilibrium constants are: K = (9.3±0.4)· 10^-6 atm(^{-$\text{1}\text{2}$}); K₁ = (2.3±0.1)·10^-2 atm(^{-$\text{1}\text{2}$}); k = 10^3.8 1 mol^-1 atm^-1 The standard potential of the system NpO₂²⁺ / NpO₂⁺ was determinedto be E⁰ = 0.220 V (vs.standard chlorine electrode).     

Synthesis and conformational behaviour of tri-3-methyltrianthranilides. A new example of spontaneous resolution and inclusion compound formation on crystallisation

The tri-3-methyltrianthranilide derivatives ($\text{7}$)–($\text{9}$) have been synthesised. Dynamic ¹H n.m.r. spectroscopy indicates that the $\text{N}$,$\text{N}$′,$\text{N}$″-trimethyl derivative ($\text{8}$) exists in solution as slowly ring inverting ($\text{16}$ ? $\text{16}$*) enantiomeric helical conformations. X-Ray crystallography shows that the $\text{N}$,$\text{N}$′-dimethyl-$\text{N}$″-benzyl derivative ($\text{9}$) undergoes spontaneous resolution when it crystallises as a 1:1 adduct from toluene. The host molecules adopt a helical conformation (Figure 1) within a lattice structure that contains chiral channels (Figure 2) occupied by guest solvent molecules.     

Polymerization in liquid crystals—IV: The polymerization of cholesteryl-vinyl-succinate

The solid-, cholesteric- and liquid-state polymerizations of cholesteryl-vinyl-succinate (CVS) are studied. Only one of the three polymorphic modifications of CVS oligomerizes in the solid state into oligomers of degree $\text{P}\text{= 2}\text{to}\text{6}$ in a homogeneous topochemical reaction. The rate of polymerization in the cholesteric state is lower than that in the liquid state at the same temperature. Kinetic constants were measured at 85° using benzoyl peroxide as initiator and the Banfield radical, giving E_overall = 15.4, 36.4 kcal/mole^?1; $\text{f = 0.52, 0.19; k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.0167, 0.0192}$, (1/mole sec)^{$\text{1}\text{2}$}, ($\text{E}{}_{\mathrm{p}}\text{?}\text{1}\text{2}\text{E}{}_{\mathrm{t}}\text{) = 0.40, 21.4}$ kcal mole^?1. The values refer to the liquid- and the cholesteric-state reactions, respectively. The average degree of polymerization is low in both cases ($\text{P}\text{= 20}\text{and}\text{22}$). It was concluded that the molecular weights are controlled by chain transfer and that the initiation reaction is mostly dependent on the phase where the reaction takes place.     

The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Über reaktionen mit aluminiumalkylen: XVII. Spektroskopische untersuchungen von komplexen aus butanoliden und äthylaluminium-verbindungen

Three different types of butanolide complexes with Et_nAlCl_3?n in the molar ratios $\text{1}\text{1}$ and $\text{1}\text{2}$ have been investigated by IR with ^1M NMR spectroscopy. The butanolides form $\text{1}\text{1}$ and $\text{1}\text{2}$ complexes with ethylaluminium halides, but with triethylaluminium only $\text{1}\text{1}$ complexes are formed. The complexes are intermediates in the cleavage of butanolides.     

Transient spectrum from nanosecond pulse radiolysis of liquid ammonia

In addition to the absorption of the ammoniated electron, the transient absorption spectrum of irradiated liquid ammonia contains two ultraviolet bands at 250 nm and 320 nm. The latter is shown to be due neither to the NH₂^? ion nor to NH singlet. There is conflicting evidence concerning its possible assignment to NH triplet. The C value of the ammoniated electron has been found to be 3.0 at ?48°C. At ?45°C, the ammoniated electron decays with concurrent first and second order kinetics and it reacts with Cu²⁺ with the rate constant 1.5 × 10¹¹$\text{l}$ mole^?1 sec^?1.