Ternäre Komplexe in Lösung IV. Einfluss von 2,2′-Bipyridyl auf Stabilität und Acidität des Cu2+-Adenosin-5′-monophosphat-N(1)-oxid-1:1-Komplexes

The ternary Cu²⁺?2,2′-bipyridyl-adenosine-5′-monophosphate-N(1)-oxide complex was investigated and compared with the binary Cu²⁺-adenosine-5′-monophosphate-N(1)-oxide complex (I) (cf. [2]). In both complexes Cu²⁺ is bound to the o-amino-N-oxide group of adenosine-5′-monophosphate-N(1)-oxide (HL). The stabilities of the complexes monoprotonated at the phosphate group are of the same order: log K = 11,20, and log K = 11,19. The acidity constants for the deprolonation of the phosphate group in these complexes are slightly different (pK = 5,55, and pK = 5,88), but as expected both values are lower than the corresponding value pK = 6,12 of the ligand.     

Über den Einfluss der pK-Werte von Anilinen auf die Bildung und Folgereaktionen von substituierten Butadienen aus Cumalinsäure-methylester

The Influence of Aniline pK Values on the Formation and Reactivity of Substituted Butadienes from Methyl Coumalate The product of the reaction between 2 equiv. of methyl coumalate ( 1 ) and 1 equiv. of a substituted aromatic amine depends on the pK value of the latter. Aromatic amines with pK values between 1.05 and 2.8 produce bicyclic lactones 4 , whereas those with higher pK values also give 2-azabicyclo[3.3.1]nona-3,7-diene-9-carboxylic acids 9 . The latter, products of the intramolecular Diels-Alder reaction 8 → 9 , may in certain cases even prevail.     

Conformational Analysis and Chromic Acid Oxidation. Oxidation Rates and Equilibrium Constants of Epimeric Alcohols

The linear free energy relationship of Sicher for relative reactivity towards chromic acid oxidation (ΔΔG) as a function of thermodynamic stability (ΔG) has been reexamined with 23 pairs of epimeric alcohols. The plot of ΔG vs. ΔG has a slope of 0.8, a correlation coefficient of 0.97 and a standard deviation of 0.23 kcal/mol on ΔΔG_Ox. The limitations of the relationship and the exceptions are discussed.     

A Unified Interpretation of Kinetic Data on the Acid-Induced Cleavage and of Product-Analysis Data on Spontaneous Cleavage of the Mono-ol Cation μ-Hydroxo-bis[pentaamminecobalt(III)] ([(NH3)5CoOHCo(NH3)5]5+)

Recent work on the spontaneous (= acid-independent) cleavage of the mono-ol cation, i.e. in Cl^?/ClO and NO/ClO mixed-electrolyte media has established (by analysis of anion-competition experiments) the existence of reactive ion pairs of the mono-ol cation with Cl^? and NO. Their existence must be allowed for in the analysis of the rate data for the acid-induced cleavage (pH 0–1) of the mono-ol cation in these mixed-electrolyte media. Thus, previous data for acidic Cl^?/ClO media have been re-interpreted in this work, and new data for NO/ClO media have been analyzed in the same sense. This analysis removes an apparent discrepancy in the orders of magnitude of ion aggregate stability constants between the mono-ol and similar binuclear cations.     

63Cu-NMR.-Untersuchungen von Kupfer (I)-Tetrapyridin-und Kupfer (I)-Tetraacetonitrilsolvaten

⁶³Cu-NMR.-Spectra of Cu(CH₃CN)₄X (X = ClO, BF, PF) and Cu(C₅H₅N)₄X (X = ClO, BF) in solution are reported at different temperatures and concentrations. The influence of temperature on the linewidth and chemical shift indicates an equilibrium of Cu(CH₃CN) and Cu(C₅H₅N) with another complex of lower symmetry. The preferential solvation of Cu (I) by pyridin in a mixture acetonitrile/pyridine is clearly shown.     

Charge Dispersal in the Quinuclidine Radical Cation and in the Quinuclidinium Ion,as Revealed by PE and ICR Spectroscopy

The n ionization energies I and the gas-phase basicities GB of CH₃-, Cl-, or CN-substituted quinuclidines have been measured by PE and ICR spectroscopy. The dependence of the shifts ΔI and ΔGB (relative to the values of the parent molecule) allow conclusions about the charge dispersal accompanying the n ionization or the protonation of quinuclidine in the gas phase. The agreement with the results of a minimal basis set ab initio calculation is excellent. Comparison of the solution pK_a values with either I or GB reveals that 2-substituted quinuclidines exhibit sizeable solvent-induced proximity effects, i.e. that the corresponding quinuclidinium ions are more acidic in solution than expected on the basis of the gas-phase basicities. This agrees with earlier results concerning 2-substituted pyridines.     

Chemistry of Superoxide Ion as Revealed by the Differential Oxidation of Arylpyruvates

Superoxide ion apparently reacts with acidic substrates via species such as O₂, HO₂, O, HO and H₂O₂. Arylpyruvates give arylacetates and arylaldehydes indicating competing nucleophilic and free radical oxidation. Benzaldehyde is further oxidized by free radical and nucleophilic dioxygen species giving benzoic acid. p-Hydroxybenzaldehyde gives the corresponding benzoic acid which is best accounted for by HO₂, since O and O₂ are without effect. Hydroquinone is also produced presumably by nucleophilic attack of HO. Replacement of the acidic hydrogen atoms by sodium changes the product distribution in accord with these findings.     

Photoelectrochemistry with Colloidal Semiconductors; Laser Studies of Halide Oxidation in Colloidal Dispersions of TiO2 and α-Fe2O3

Aqueous sols of TiO₂ (anatase, particle radius 25 Å) were excited with (347.1 nm)-laser light and the reaction of valence-band holes with halide ions (X = I^?, Br^?, Cl^?) was investigated. Hole transfer takes place within the duration of the (10 ns)-laser pulse and results in the formation of anion radicals according to the sequence: The quantum yield of X increases in the order Cl < Br < I, attaining 0.8 for I at pH 1. It is affected by pH, halide concentration and the presence of a protective agent for the sol. RuO₂ deposited onto TiO₂ enhances markedly Cl and Br -formation, but has no effect on the yield of I. Laser-photolysis investigation of halide oxidation were also carried out with colloidal Fe₂O₃ (particle radius 600 Å). For I_2?formation, the quantum yield exceeds 0.9 indicating almost quantitative hole scavenging by iodide.     

Réactions de substitution dans l'anion tétrachloropalladate(II) avec des diamines. I. Ethylènediamine

The replacement of Cl^? by ethylenediamine (en) in PdCl has been followed spectrophotometrically at 25°C and μ = 1 (NaClO₄); it proceeds in two steps leading to Pd(en)Cl₂ and Pd(en), respectively. The observed rate constants are discussed in terms of the mechanism proposed by Reinhardt [1] for the successive ammination reactions of PdCl.     

Molecular Ions of Transient Species: Vinyl-Alcohol Cation

Vinyl alcohol 1 was prepared by thermolysis of cyclobutanol and its photoelectron spectrum was determined. I = 9.18 eV and I = 9.52 eV were found, the vibrations progression (? = 1400 cm^?1) for this lowest energy transition 1(X)→1⁺(X?) indicating significant skeletal changes in the ion. The question of the relative stability of the syn ( 1 )- vs. anti-ions ( 1 ) is discussed in the light of theoretical calculations. The energy of the second π-state of 1 ⁺ is estimated at 13.6–14.1 eV above the ground state of 1 .     

Molecular Recognition in Anion Coordination Chemistry. Structure,Binding Constants and Receptor-Substrate Complementarity of a Series of Anion Cryptates of a Macrobicyclic Receptor Molecule

The crystal structures of four anion cryptates [X^? ? BT -6H⁺] formed by the protonated macrobicyclic receptor BT -6H⁺ with F^?, Cl^?, Br^? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F^?-ion is tetracoordinated, while Cl^? and Br^? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H⁺ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H⁺ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP^2?, ADP^3?, ATP^4?, P₂O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F^?, Cl^?, Br^?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H⁺ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered.     

Contribution à l'étude du système quaternaire K+?NH4+?CrO?SO?H2O: II. L'isotherme de 25°C

The study at 25°C of the system K⁺? NH? CrO? SO? H₂O has shown experimentally the existence of a new type of quaternary system of solubility with two cations and two anions. The solubility diagramm is caracterized by the presence of two adjacent ternary limiting systems with a miscibility gap, three univariant lines (one of them being evanescent), one invariant point, three binary and one ternary miscibility gaps.     

Metal Complexes with Macrocyclic Ligands. XI. Ring size effect on the complexation rates with transition metal ions

The 12-16 membered tetraazamacrocycles 1 - 6 were synthesized, their protonation constants and complexation kinetics measured at 25° and I = 0.50. The results of Table 1 Show that pK is strongly influenced by the ring size whereas pK and pK are relatively insensitive to it. This can be understood in terms of electrostatic interactions of the positive charges when located on adjacent amino groups. The kinetics of complex formation between the macrocyclic ligands and several transition metal ions have been studied by pH-stat and stopped-flow techniques and the results have been analyzed as bimolecular reactions between the metal ion and the different protonated species of the ligands. The rate constants, given in Table 2, show that the macrocycles react less rapidly than analogous open chain amines. However, for a given protonated species of the ligand the rate of complexation follows the order Cu²⁺ > Zn²⁺ > Co2⁺ > Ni²⁺ which parallels the sequence of their water exchange rates. For the diprotonated tetraamines LH reacting with Cu²⁺ the slower rates seem to be mainly a consequence of electrostatic interactions, since a correlation between logk and pK exists. For LH⁺, however, the complexation rates of a metal ion with the different macrocycles are all in one order of magnitude and do not depend in a regular way on the ring size or the basicity of the ligand. It is therefore suggested that in this case other factors such as unfavourable preequilibria must be considered as important.     

A Lipophilic Derivative of Vitamin B12 as Selective Carrier for Anions

Incorporation of the lipophilic Co(III)-cobyrinate octadecyl-cobester 1 and of its ionic aqua-cyano perchlorate derivative 2 into poly(vinyl chloride)/bis(1-butylpentyl) adipate liquid membranes induces a selectivity, measured potentiometrically, of about 10³ for SCN^? an NO with respect to CI^?, but only of about 4 for ClO vs. CI^?. This is in contrast to classical anion-exchanger membranes, which exhibit a selectivity sequence ClO > SCN^? ? NO > Cl^? in accordance with the Hofmeister, series. The Co(III)-corrins 1 and 2, when components in solvent polymeric membranes, undergo exchange of axial ligands an behave as highly selective carriers fof SCN^? and NO.     

L'action de l'ammoniac sur l'hydroxyde de cadmium et la stabilité des complexes en milieu aqueux

The solubility of precipitated Cd(OH)₂ was determined at 25°C in 1 M NaClO₄, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH⁺, Cd(OH)₂, Cd(OH), CdNH, Cd(NH₃), Cd(NH₃), Cd(NH₃) and Cd(OH)₂NH₃. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration.     

The Gas-Phase Ion/Molecule Reactions of C3H5X (X = C1, Br,I)

The ion/molecule reactions of the molecular ion, the C₃H ion, and the C₃H ion obtained from 3-chloropropene. 1-bromopropene, 2-bromopropene, 3-bromopropene, bromocyclopropane. and 3-iodopropene have been studied with their neutral precursor in a Fourier-transform mass spectrometer (FT/ICR). The molecular ions react to yield primarily C₆H except for the ion derived from 1-bromopropene that is unreactive. The kinetics of the 3-bromopropene molecular ion reveals that 18% of these ions must possess a different structure which is unreactive. The fact that C₃H ions obtained from 2-bromopropene are the only ones to undergo proton transfer is taken as evidence that only this parent compound gives rise to 2-propenyl cations by low-energy electron impact. The C₃H ions generated in these systems are shown to be roughly an equal mixture of propargylium ions that react to yield C₆H and unreactive cyclopropenium ions.     

Endohedral fullerene-noble gas clusters formed with high-energy bimolecular reactions of C (x = 60, 70; n = 1, 2, 3)

Results are reported for high-energy beam experiments which establish the formation of endohedral carbon cluster-noble gas compounds by bimolecular reactions of C (x = 60, 70; n = 1, 2, 3) with He and C with Ne. The ions were accelerated up to 8 ke V in a four-sector mass spectrometer and allowed to collide with the noble gas in a collision chamber at room temperatur. Product ions were monitored with a B/E = constant linked scan. Within the sensivity of the experiments, no carbon cluster-gas compounds were observed in the reactions of C with H₂, D₂, O₂, Ar, and SF₆, or of C with O₂. The observed fall in the cross-section for carbon cluster-noble gas compounds with increasing size of the noble gas, the observation of unimolecular loss of C₂ from mass-selected C_xHe⁺ ions, and the elimination of carbon fragments instead of He observed in the formation of the collision-induced C_xHeⁿ⁺ product ions are taken as evidence for endohedral compound formation. Results of ab initio molecular-orbital calculations for the perpendicular penetration of the plane of ionized benzene with He, Ne, and Ar indicate that sufficient kinetic energy should be available in the collisions with C to penetrate the C cage at the collision energies of the experiments.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Etude cinétique de la réaction de bromation d'anisoles monosubstitués. Transmission des effets électroniques et caractéristiques de l'état de transition

Reactivity-structure correlations for anisole and eleven of its substituted derivatives established from bromination rate constants in liquid SO₂, unlike observations in water, show the reaction to be highly sensitive to substituent effects, (ρ = ?7.1; ρ = ?10.51). This result is ascribed to the solvation of the methoxy group which decreases the conjugation of para-substituted (ρ = ?9.70) compared to that of ortho-substituted derivatives (ρ = ?8.86). The highly solvated transition state lies far from reactants on the reaction coordinate and the positive charge developed in this state is nearly unity.     

On the Basicity of Triarylmethylamines in Solution

The pK of 11 triarylmethylamines (tritylamines), eight of which are new, and some related bases were measured in methylcellosolve/water 80:20 (MCS); some were also measured in dioxane/water 60:40 (Dx), acetonitrile (An), nitrobenzene (Nb) and acetic acid (Ac). (1) The influence of the aryl groups on the basicity is essentially additive; (2) In different solvents, similar linear free energy relationships were found, with differences in p* characteristic of solvation; (3) The influence on basicity of substituents of the aryl groups follows Hammett's relationship. These results indicate a preponderance of inductive effects. N, N-Dimethyltritylamine (3b) (pK=3.40) shows a marked crowding effect, absent in the isomeric tertiary amines 13 and 14 . Tri-p-nitrotritylamine (10a) (pK=3.10), N, N-dimethyl-tri-p-nitrotritylamine (10b) (pK=0.50), and 3b are particularly weak bases; the base-weakening effect of the trinitrotrityl group is similar to that of the cyanomethyl and trifluoroethyl groups.     

L'action de l'ammoniac sur l'oxyde cuivrique. et les hydroxo-complexes de cuivre (II)

Using a new mathematical treatment, the nature and stability constants of the simple and mixed complex-species of copper(II) with hydroxyde and ammonia as ligands have been determined. The solubility curves of CuO in heterogeneous equilibrium have been identified in function of pH only and in function of pH and pNH_3tot at 25° and unit ionic strength (NaClO₄). The predominent species in the relatively dilute system limited by the ionic strength are [Cu²⁺], [Cu(OH)₂], [Cu(OH)], [Cu(OH)], [Cu(NH₃)], [Cu(NH₃)], [Cu(NH₃)], [Cu(NH₃) (OH)⁺], [Cu(NH₃)₃(OH)⁺] and [Cu(NH₃)₂(OH)₂].