Showing papers by "Indian Association for the Cultivation of Science published in 1972"

Effect of amines on the ceric ion‐initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

Abstract: The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate Rp is independent of ceric ion concentration and can be expressed by the equation: Rp = k1 [amine] [monomer] + k2[monomer]2, where k1 and k2 are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.

Application of dye techniques in the study of chain‐transfer properties of thiols

Abstract: Dye techniques (dye partition technique in particular) have been found to be simple and sensitive methods for studying the chain transfer properties of substituted thiols containing ionic or ionogenic groups (amenable to dye test). These are: 2-Mercapto ethanol, 2-mercapto ethylamine hydrochloride, and thioglycolic acid. Ctr values obtained by this method are found to agree fairly well with those obtained from conventional DP methods. ARRHENIUS parameters and some thermodynamic functions have been evaluated from experimentally determined Ctr values. Existence of a negative temperature coefficient is found for the transfer process of the thiols with PMMA radicals. Transfer potency of the thiols is found to be dependent on their structure. Thus Cs value for 2-mercapto ethylaminehydrochloride with MMA is found to be least in the present series which can be accounted for the presence of a strong electron accepting group in the thiol which vehemently opposes the electron transfer from the thiol to the electron accpeting PMMA radical in the transition state. Anfarbetechniken, insbesondere die Farbverteilungstechnik (Dye-partition technique), haben sich als einfache und empfindliche Methoden bewahrt, um die Kettenubertragungseigenschaften substituierter Thiole mit ionischen oder ionogenen Gruppen zu untersuchen. Verwendet wurden: 2-Mercaptoathanol, 2-Mercaptoathylaminhydrochlorid und Thioglykolsaure. Mittels dieser Methode erhaltene Ctr-Werte stimmen ziemlich gut mit jenen uberein, die man mit den ublichen DP-Methoden erhielt. Aus den experimentell bestimmten Ctr-Werten wurden Parameter nach ARRHENIUS und einige thermodynamische Funktionen berechnet. Die Ubertragungsreaktion der Thiole mit PMMA-Radikalen hat einen negativen Temperaturkoeffizienten. Die Ubertragungsfahigkeit der Thiole ist strukturabhangig. So ist der Cs-Wert von 2-Mercaptoathylaminhydrochlorid mit MMA unter den untersuchten Verbindungen der kleinste, was mit der stark elektronenanziehenden Gruppe im Thiol erklarbar ist, die der Elektronenubertragung aus dem Thiol auf das PMMA-Radikal im Ubertragungszustand entgegen wirkt.

Kinetics and mechanism of dissociation of bis(biguanide)‐Palladium(II) Ion in HCl ? NaCl Medium

Abstract: The kinetics of the stepwise dissociation of bis(biguaniide)palladium (II) ion in HCl—NaCl media have been studied spectrophotometrically. The first step leads to the formation of dichloromono(biguanide)palladium(II) at low acid concentrations (0.01–0.1 M HCl); the second step leads to the formation of tetrachloropalladate(II) ion at higher acid concentrations (0.15-0.4 M HCl). There are two concurrent reaction paths in each step, one of which is first order with respect to both H+ and Cl− ion concentrations, while the other is second order with respect to both. The individual rate constants have been evaluated, as well as the corresponding activation parameters, ΔH≠ and ΔS≠, and possible mechanisms have been discussed. Kinetik und Mechanismus der Dissoziation des Bis(Biguanid)palladium(II)-Ions in HCl–NaCl-Losungen. Die Kinetik der stufenweisen Dissoziation des Bis(biguanid)-palladium(II)-Ions in HCl–NaCl-Losungen wurde spektrophotometrisch untersucht. Der erste Schritt in schwach saurer Losung (0,01–0,1 m HCl) fuhrt zur Bildung von Dichloromonobiguanid-palladium(II), der zweite Schritt in starker saurer Losung (0,15–0,4 m HCl) zum Tetrachloropalladat(II)-Ion. Bei jeder Stufe liegen zwei Konkurrenzreaktionen vor, eine von erster Ordnung, die andere von zweiter Ordnung. Die einzelnen Geschwindigkeitskonstanten und die entsprechenden Werte von ΔH= und ΔS= wurden ermittelt, ein moglicher Reaktionsmechanismus wird diskutiert.

Mixing of 3d and Excited Orbitals of an Iron Group Ion in a Tetrahedral Field and Its Effect on Orbital Momentum and Spin-Orbit Coupling Coefficient

Abstract: Mixing of 3d and excited orbitals such as 4p, 4d, and 4f of an ion via crystal field and the effect of this mixing on the orbital moment and the spin-orbit coupling coefficient have been discussed for the case of iron-group complexes of tetrahedral coordination. It has been shown that the admixture of excited orbitals to the 3d orbitals effectively reduces the orbital moment and S—O coefficient with respect to the values corresponding to pure 3d orbitals. These reductions have been estimated for different ions of tetrahedral coordination within the framework of crystal field theory. The reduction of the S—O coefficient is found to be larger than that of the orbital moment. It has been inferred that in some of the ions the reductions due to the admixture of excited metal orbitals may not be negligible when compared with those produced by the covalency effect although the latter, in general, causes a larger reduction of the two parameters.

Covalency reduction factors in C4v and D3h and estimation of bonding parameters from magnetic data

Abstract: The covalency effect in the complexes of the iron group reduces the orbital angular momentum and the spin-orbit coupling constant from their respective free ion values. Recent interest in penta-coordinated complexes suggested the derivation of the expressions for the orbital and spin-orbit coupling reduction factors in complexes of D3h and C4v symmetry. With the help of these expressions and using Slater functions for the radial integrals involved therein the bonding parameters representing the degree of covalency have been estimated from the available magnetic data in the two cases. Der Kovalenzeffekt in Komplexen der Eisengruppe reduziert den Bahndrehimpuls und die Spin-Bahnkopplungskonstante gegenuber den entsprechenden Werten des freien Ions. Neuerliches Interesse an Komplexen mit Funferkoordination waren bestimmend fur die Ableitung der Reduktionsfaktoren des Bahndrehimpulses und der Spin-Bahnkopplung in Komplexen mit D3h- und C4v-Symmetrie. Mit diesen Ausdrucken und Slaterfunktionen fur die hierbei benotigten Radialintegrale wurden die Bindungsparameter. die den Grad der Kovalenz darstellen, aus erhaltlichen magnetischen Daten in den beiden Fallen berechnet.

Lattice—Ion Interactions in the Ligand Field Theory of Trigonally Distorted Octahedral V3+ Complexes

Abstract: The theoretical expressions for the magnetic susceptibility and g-values of trigonally distorted octahedral V3+ ion have been developed on the basis of molecular orbital method of Stevens [19] and Bose et al. [20]. Results are discussed considering the less strong vibronic coupling (dynamic Jahn-Teller effect) in which an orbital triplet interacts with the vibrational E-modes of the ligands. Comparison is made with experimental results on magnetic susceptibility, g-values, and optical absorption with a unique set of values of parameters in the theoretical expressions at all temperatures. The Jahn-Teller coupling parameter appears to be appreciable in some of the complexes. Die theoretischen Ausdrucke fur die magnetische Suszeptibilitat und die g-Werte trigonal gestorter oktaedrischer V3+ -Ionen werden auf der Basis der Molekulbahnen-Methode von Stevens [19] und Bose et al. [20] entwickelt. Die Ergebnisse werden unter Berucksichtigung der weniger starken vibronischen Kopplung (dynamischer Jahn-Teller-Effekt) diskutiert, wobei ein Bahntriplet mit den vibronischen E-Moden der Liganden in Wechselwirkung tritt. Die experimentellen Ergebnisse der magnetischen Suszeptibilitat, der g-Werte und der optischen Absorption werden mit einem eindeutigen Satz von Parameterwerten in den theoretischen Ausdrucken bei allen Temperaturen verglichen. Der Jahn-Teller-Kopplungsparameter scheint in einigen Komplexen von Bedeutung zu sein.

Polarographic behaviour of quinoxaline-2-carboxylic acid and its derivatives at the dropping mercury electrode and amperometric determination of copper, zinc, cobalt and nickel with quinoxaline-2-carboxylic acid

Abstract: The polarographic behaviour of quinoxaline-2-carboxylic acid and some of its derivatives (3-chloroquinoxaline-2-carboxylic acid, 3-hydroxyquinoxaline-2-carboxylic acid and quinoxaline-2∶3-dicarboxylic acid) at the dropping mercury electrode has been described. The reagents are all found to be polarographically reducible, the E1/2 values being shifted to more negative potentials with increase in pH. Wave-heights have been found to be proportional to the concentration of the reagents down to 2×10−4 M. The reactions are not perfectly reversible.

On the Inversion from the Energy Dependence of Total Cross-Sections

Abstract: The suitability of a recently suggested method for the inversion from the energy dependence of total cross-section data at high energies has been critically examined by considering He-He system. For this purpose, the data had to be generated partially by theoretical calculations. The results of the analysis show that the method has excellent potentialities, provided the required experimental data are available. Some suggestions for performing such experiments have been given.