Equilibrium Constants For Formation Of Complexes Research Articles

Pulsradiolyse organischer Halogenverbindungen I. Nachweis kurzlebiger Charge‐Transfer Komplexe mit Chloratomen

AbstractIn a solution of benzene in carbon tetrachloride a transient absorption in the visible part of the spectrum could be detected. It appears within less than 0.3 μs after the irradiation by a high‐energy electron pulse, and it can be shown to be due to the charge‐transfer complex between the chlorine atoms as electron acceptors and benzene molecules as electron donors. A variety of aromatic hydrocarbons also yield similar absorption bands in the visible. They show a linear correlation between the absorption energy and the ionisation potential of the aromatic molecules, which is typical for charge‐transfer complexes. A minimum value for the equilibrium constant of complex formation is given. The equilibrium is almost fully shifted to the complex side. An estimated G value for the charge‐transfer complex indicates that the complex is actually part of a main reaction in the radiation‐induced mechanism. The decay of the charge‐transfer complex is mostly pseudo‐first order with a half life of a few microseconds.

Chemical shifts for compounds of the group IV elements silicon and tin

Chemical shifts for 29Si in seven series of molecules of the type XnSiY4−n have been measured where Y is an alkyl group and X varies widely in electronegativity. A considerable amount of proton and fluorine chemical shift data has been obtained for the same compounds and in one series (CH3)nSiCl4−n the 13C chemical shifts in the methyl groups have been measured.The gross features of the 29Si chemical shifts are understood by considering the series (Alkyl)3SiX with the electronegativity of X widely varied. The hybridization at silicon is approximately conserved in these series and the theoretically anticipated linear dependence on electronegativity of X is demonstrated. The ligands X = O, N, and F are exceptional and these 29Si chemical shifts have a high field shift. This additional shielding has been associated with (p → d)π bonding. The approximate nature of present chemical shift theories is not likely to provide a measure of the order of (p → d)π bonding.The 29Si chemical shifts in the series XnSiY4−n are discussed and also indicate a net shielding effect with (p → d)π bonding. A comparison is always made with corresponding 13C chemical shifts. A long range proton–proton coupling in molecules Me3SnX and Me2SnX2, H—C—Si—C—H, is observed when and only when X = O, (N?), F.119Sn chemical shifts in a series of alkyltin compounds have been measured. The same dependence on the electronegativity of X in the series (Alkyl)3SnX is noted, but the variation of X is much more limited. Some shielding due to (p → d)π bonding in the series (n-Butyl)nSnCl4−n is suggested. The tin chemical shift has been measured as a function of concentration and solvent for simple methyltin bromides and chlorides. In donor solvents, it has been possible to obtain equilibrium constants for complex formation from tin dilution chemical shifts. The nature of the bonding in complexes suggested previously is consistent with the variations in the coupling constant |JSn–C–H| with concentration. The distinction between ionization and complex formation with the solvent for (CH3)2SnCl2 can be made on the basis of the concentration dependence of |JSn–C–H|The spin–lattice relaxation time T1for 13C and 29Si in natural abundance in several pure degassed compounds has been measured. These are not in the case of 13C (as has been suggested) of the order several minutes, but are always less than 50 s and in one case as low as 3–4 s. Both 29Si and 13C T1 values follow what might be expected on the basis of a dipole–dipole mechanism from the closest protons. The short value of 35 s in CS2 is probably a result of spin–rotation interaction in the liquid state.

Charge-transfer interaction of dithienyls and cyclopentadithiophenes with 1,3,5-trinitrobenzene (TNB)

The equilibrium constants for complex formation of the isomeric dithienyls (I–III), three of the six possible flat (rigid) cyclopentadithiophenes (IV–VI), 1,3 thiophene and the methylthiophenes with 1,3,5-trinitrobenzene (TNB) in cyclohexane have been measured by a spectroscopic method. The relative stabilities as well as the thermodynamic properties suggest almost free rotation of the thienyl rings around the central C bond for the dithienyls. Crystalline complexes of the dithienyls and of their flat analogs have been prepared. Finally the ionization potentials (I D ) of the several donors (including the isomeric dithenyl-methanes 3,4) have been calculated using the known relationship with the hv max of the charge transfer bands.

The ionization energies of some phenothiazine tranquillizers and molecules of similar structure

Charge-transfer spectroscopy was used to determine the ionization energies of ten phenothiazine tranquillizers and similar molecules which are stimulants, in order to throw light on the proposed relation between physiological action and electron-donating power, and to compare the ionization energies of the phenothiazines with molecular orbital calculations. All the ionization energies obtained lie in the range 7.0-8.4 eV. The phenothiazines are thus strong electron donors, in agreement with calculations. There is little difference in ionization energies and equilibrium constants of complex formation between tranquillizers and either non-tranquillizers or stimulants. The difference in physiological action of the drugs therefore cannot be dependent on electron-donating power alone.

Cyanide complex of 1,3,5-trinitrobenzene in nonaqueous solvents

The initial reversible interaction of 1,3,5-trinitrobenzene and cyanide ion has been studied spectrophotometrically in a number of nonaqueous solvents and found to result in the formation of a complex containing 1,3,5-trinitrobenzene and cyanide ion in a 1:1 ratio. At 25.3 °C, the equilibrium constants for complex formation (K) and the molar extinction coefficients (ϵ) of the complex were found to be 1.44 ± 0.15 × 105 l mole−1 and 2.24 ± 0.05 × 104 l mole−1 cm−1 and 3.35 ± 0.35 × 105 l mole−1 and 2.24 ± 0.05 × 104 1 mole−1 cm−1 respectively for acetone and chloroform solutions. The second-order rate constant governing formation of the complex in chloroform was found to be 2.25 × 102 l mole−1 s−1 at 25.0 °C. On the basis of the visible and infrared absorption data obtained for the complex in chloroform and 1,2-dimethoxy-ethane, the complex is considered to be a Meisenheimer-type complex rather than a "charge-transfer" complex.

Charge-Transfer Complexes of Carbonyl Cyanide in Gas and Condensed Phases

Absorption spectra of carbonyl cyanide charge-transfer complexes with common donors were studied in gas phase and in solutions, their fluorescence spectra in n-hexane solutions at 77°K. The general form of the absorption band is the same in the gas and liquid phases, but the gas-phase spectra show a blue shift of 2000–3500 cm−1, an intensity decrease, and a strong increase in the equilibrium constant of complex formation. The reasons of the frequency shift, the splitting of absorption bands, and the influence of complex formation on the electronic spectrum of carbonyl cyanide are discussed.

Ultraviolet spectra and complex formation in mixtures of polar organic solvents and aromatic hydrocarbons

Ultraviolet spectra at 25°C have been measured for mixtures of p-xylene and thirteen polar organic solvents dissolved in n-hexane. The data support the hypothesis that weak complexes are formed between aromatic hydrocarbons and such common polar solvents as aliphatic ketones, nitroparaffines and nitriles. When reduced with D rago's equation the spectral data yield equilibrium constants for complex formation in the range 0.03–0.3 liters/gmol.

Studies on Mixture Dyeing. III. The Absorption Spectra of Direct Dye Mixtures in an Aqueous Solution

Abstract The absorption spectra of a binary mixture of five representative direct dyes in solution have been investigated. The equilibrium constants for complex formation are in the 107–104 range and are in the order: Chrysophenine G - Sky Blue 6B>Benzopurpurine 4B - Sky Blue 6B>Sirius Red 4B - Sirius Supra Blue BRR>Sirius Red 4B - Sky Blue 6B= Benzopurpurine 4B - Sirius Supra Blue BRR>Chrysophenine G - Sirius Supra Blue BRR. The combination of Chrysophenine G and Sky Blue 6B is a typical one in direct dyes. The equilibrium constant for an aggregation of like dye molecules is very much smaller than the value of 104 at room temperature.

1172. The study of the equilibrium constant of complex formation between phenol and pyridine in solution by a dielectric constant method

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The recombination of atoms, IV. Iodine atom complexes

Transient absorption spectra have been detected after flash photolysis of iodine in a variety of solvents. There is some correlation between the wavelength of maximum absorption and the ionization potential of the solvent and the spectra are attributed to the charge transfer complexes between iodine atoms and the solvent which were predicted in part III. In the case of methyl iodide as chaperon a weak transient has also been observed in the vapour phase. The decay of the complex follows a second-order law and rate constants have been measured in six solvents. Values for the extinction coefficient are derived by assuming that the reaction is diffusion controlled. Equilibrium constants of complex formation have been measured in ethyl iodide and ethyl bromide.

Reaction of ferrimyoglobin with phenols.

IF, in a haemoprotein, the haem iron atom is held by bonds to the protein on both sides of the porphyrin ring, then the most likely mechanism for complex formation with the ligands CO, NO, F−, CN−, N3 −, etc., entails breaking the weaker bond while leaving the stronger bond intact. The proton affinity of the group thus liberated would be an important factor in determining the pH variation of the equilibrium constants for complex formation. The limited extent to which such a mechanism can account for haem-linked ionizations in haemoglobin reactions, its direct application to cytochrome c reactions, and the way it can account for some of the differences found in peroxidase and catalase reactions have been discussed recently1,2. The question naturally arises whether any other functional groups in amino-acid side-chains can co-ordinate with the iron beside nitrogenous base groups, which in cytochrome c give rise to the characteristic haemochromogen and parahaematin spectra that set it apart from the other ferro- and ferri-haemoproteins. Internal complex formation is a possibility in the ferric oxidation state via—COOH, alcoholic —OH and —SH groups in the side-chains, since complexes are known to be formed between ferrihaemoglobin and formic acid, acetic acid, propionic acid, ethanol, hydrogen sulphide and ethyl mercaptan3–6. Furthermore, the following preliminary report on the reaction of ferrimyoglobin with phenols shows that the phenolic —OH group can be added to this list.

4:6-dinitrobenzofuroxan, nitrobenzodifuroxan and benzotrifuroxan: A new series of complex-forming reagents for aromatic hydrocarbons

4:6-Dinitrobenzofuroxan, 5:6-dinitrobenzofuroxan, nitrobenzodifuroxan and benzotrifuroxan have been prepared, and the values of the equilibrium constants for complex formation between naphthalene and this series of compounds have been determined in chloroform solution. Benzotrifuroxan has yielded solid complexes with a wide range of aromatic hydrocarbons.

The interaction of steroid hormones and coenzyme components

1. 1. The distribution-equilibrium method has been refined to permit the measurement of equilibrium constants for complex formation between several steroids and coenzyme components in aqueous solution. 2. 2. From the relation of the structure of the steroid and the coenzyme component to the equilibrium constant, it is concluded that complexes result from interactions between the purine nucleus of coenzyme components which contain purines, and the α-side of rings, C, D, and part of ring B of the steroid. The flatness of this region of the steroid is of primary importance for complex formation. Interactions found to occur with riboflavine phosphate are presumably of a similar type. 3. 3. The nature of the forces leading to complex formation are discussed. The interaction appears to be of a non-polawr character, most of the energy being derived from the recombination of water molecules which are displaced from the interacting surfaces.