Showing papers in "ChemInform in 1974"

Thermodynamics of electrolytes. IV. Activity and osmotic coefficients for mixed electrolytes

Abstract: An equation has been developed with the guidance of recent statistical theories of electrolytes which is designed for convenient and accurate representation and prediction of the thermodynamic properties of aqueous electrolytes including mixtures with any number of components. The three previous papers have given the theoretical background and the evaluation of parameters for pure electrolytes of various charge types. The equation is here applied to a wide variety of mixed aqueous electrolytes at room temperature and at ionic strengths up to 6 M in many cases and occasionally even higher. The first objective is the prediction of properties of mixed electrolytes using only the parameters for pure electrolytes; on this basis standard deviations in ln ..gamma.. or phi for 69 sets of mixtures are less than 0.01 in 36 cases and above 0.05 in only seven cases all involving Cs/sup +/ or OH/sup -/. A second objective is the determination of parameters giving the differences in short-range interaction of ions of the same sign where these differ significantly from zero. As expected, these difference terms, while always small, are relatively most important for singly charged ions (and especially for OH/sup -/ and Cs/sup +/) and less important for ions ofmore » higher charge. The equations, including difference terms where known from binary mixtures with a common ion, were finally tested on 17 sets of mixtures involvingfour or more ions without any further adjustment of parameters. The standard deviation is less than 0.01 in all cases and is 0.003 or less in 11 cases. Thus these equations appear to yield accurate predictions of properties of mixed aqueous electrolytes. 5 tables.« less

Specific Rate Constants of Unimolecular Processes II. Adiabatic Channel Model

Abstract: The rate of unimolecular processes is calculated by means of a statistical adiabatic channel model. The rates are mainly determined by the maxima of the channel energies. The channels are constructed by correlating reactant and product states; the channel energies are computed by a simple interpolation procedure. The coupling between the various vibrational-rotational motions is taken into account. The influence of parameters of the potential surface on channel energies and on rate constants is studied. Numerical results for the NO2, CH4, CD4, C2H6 and C2D6 dissociation – recombination kinetics are compared to experimental data. The statistical adiabatic channel model gives similar results as minimum local entropy models. Both these approaches lead to stronger curvatures of k(E) and smaller activation energies for the thermal rate constant k∞ than the corresponding RRKM calculations. Die Geschwindigkeit unimolekularer Zerfallsreaktionen wird mit Hilfe eines Modells adiabatischer Kanale statistisch berechnet. Wesentlich fur die Reaktionsgeschwindigkeiten sind die Maximalenergien der Kanale, die durch Korrelation von Zustanden der Reaktanten und Produkte und einfache Interpolation bestimmt werden. Die Kopplung der Schwingungs-Rotationsbewegungen wird beachtet. Der Einflus von Potentialflachenparametern auf Kanalenergien und Geschwindigkeitskonstanten wird studiert. Numerische Ergebnisse fur die Dissoziations-Rekombinationskinetik von NO2, CH4, CD4, C2H6 und C2D6 werden mit experimentellen Daten verglichen. Das Modell adiabatischer Kanale ergibt ahnliche Ergebnisse wie Modelle mit aktivierten Komplexen, die an Stellen minimaler Zustandsdichte lokalisiert werden. Beide Ansatze fuhren zu einer starkeren Krummung der k(E)-Kurven und zu geringeren Arrhenius-Aktivierungsenergien fur die thermischen Geschwindigkeitskonstanten k∞ als entsprechende RRKM Rechnungen.

Palladium-catalyzed formylation of aryl, heterocyclic, and vinylic halides

Abstract: Die Bromide (I) werden in Gegenwart von Tri-n-butyl- oder Triathylamin und dem Pd-Komplex (II) mit einem CO-H2-Gemisch bei 80 bis 150°C uber die sich wahrscheinlich zunachst bildenden Organo-Pd-Verbindungen zu den Aldehyden (III) formyliert.

Noble metal catalysis. III. Preparation of dialkyl oxalates by oxidative carbonylation

Abstract: Die Synthese von Diathyloxalat (IV) in Alkoholen unter Zusatz von Edelmetallkatalysatoren und Oxidationsmitteln wird untersucht.

The synthesis and ion binding of synthetic multidentate macrocyclic compounds

Abstract: Der Ubersichtsartikel behandelt makrocyclische Verbindungen wie Kronenather, z.B. (I) und polycyclische Amine, z.B. (II), sowie Makrocyclen, die Stickstoff und Sauerstoff und Schwefel oder Stickstoff und Schwefel enthalten.

Advances in Homolytic Substitution of Heteroaromatic Compounds

Abstract: Publisher Summary The most interesting development in the field of homolytic aromatic substitution is the realization that polar effects in several reactions play a role important based on the transiton state. The extent of these effects is determined by both the nature of the free radicals and the reacting substrates so that strong polar effects were observed not only with strongly polar radicals, but also with moderately polar radicals, such as carbon-free radicals, if the reacting substrate has a marked polar nature. Homolytic animation is of great interest in the homocyclic aromatic series with a selectivity and versatility comparable to that of electrophilic substitution. Homolytic substitutions with nucleophilic radicals are of great importance for protonated heteroaromatic bases but of lesser interest using nonprotonated heteroaromatic bases and homocyclic aromatic substrates. Among these nucleophilic radicals the use of alkyl, acyl, carbamoyl, α-oxyalkyl, and α- N -alkyl radicals has proved to be very successful. The aryl radicals were used in obtaining a deeper understanding of the homolytic arylation of heteroaromatics, but the sensitivity to polar effects is too low to give significant selectivity from the synthetic point of view.

Advances in Oxazole Chemistry

Abstract: Publisher Summary This chapter discusses advances in oxazole chemistry. A significant interest in the chemistry of oxazole was revived in an effort to synthesize penicillin, when this fascinating antibiotic molecule was thought to contain an oxazole ring. In this way, aspects of oxazole chemistry are studied which had received little or no attention before. The chapter explores the numerous developments made in the field of oxazole chemistry from the beginning of 1955 to the end of 1972. The emphasis has been placed on methods of synthesis and reactions of the mononuclear oxazoles; therefore, only a few references are given to condensed oxazoles (such as benzoxazoles and naphthoxazoles). The formation of oxazoles generally predominates at around 130oC when slightly more than a molar quantity of formamide is used. The oxazole synthesis is about equally successful when α-halo ketones are boiled with a mixture of ammonium formate and formic acid (large excess) in place of formamide and concentrated sulfuric acid.

Heterobihalide ions. Nuclear magnetic resonance spectroscopy of strong hydrogen bonds

Abstract: Die 1H- und 19F-NMR-Spektren der Ionen FHX(-) (X = F, Cl, Br, J) werden gemessen und die Kopplungskonstanten ermittelt.

Polarity of van der waals molecules

Abstract: The polarity of a number of loosely bound complexes is qualitatively measured by molecular beam electric deflection. The following species are observed as polar: ArNO, ArHCl, NeDCl, XeHCl. ArBF/sub 3/, KrBF/sub 3/, (NO)/sub 2/, (HCl)/sub 2/, BF/sub 3/NO, BF/sub 3/CO, (CO/sub 2/)/sub 2/, Among the species observed to be nonpolar are: (NO)/sub 3/, (NO)/sub 4/, N/sub 2/0/sub 2/, NeHCl, COH/sub 2/, (BF/sub 3)/sub 3/, (BF/sub 3/)/sub 4/, (BF/ sub 3/)/sub 4/. Structural interpretations of these results, together with some preliminary radiofrequency spectroscopy, are presented.

Initiation of pitting at sulfide inclusions in stainless steel

Abstract: Equilibrium calculations on some sulflde systems actual in commercial stainless steel have shown that the sulfides cannot thermodynamically exist at the potential of the passive steel. The ions released by the dissolution of the sulfides give rise to an acid solution in microareas. A pitting corrosion mechanism based on the sulfides themselves is suggested. The sulfides are polarized to the potential of the passive steel surface and tend to dissolve. During the dissolution a virgin metal surface is exposed to the environment. When the solution in the microarea thus developed has reached a certain composition, the contacting metal can no longer passivate and the metal starts to dissolve.

1-, 2-, and 3-Benzazepines

Abstract: Publisher Summary This chapter discusses 1-, 2-, and 3-Benzazepines. Ring closure with the formation of a carbon-nitrogen bond, of the types A-E shown in the chapter, has been used to synthesize derivatives of 1-, 2-, and 3-benzazepines, with aminocarboxylic acids, amino halides, dihalides, dinitriles, dicarboxylic acids, and carboxylic acid diamides as starting materials. The yields are generally fair to good. In some cases, preferential formation of a five- or six-membered ring is observed. The formation of a carbon-carbon bond to construct the seven-membered ring of the benzazepines has been achieved by ring closures of the types F-L. The Friedel-Crafts reaction (limited in the 1-benzazepine series), Dieckmann, acyloin, and aldol condensations, Bischler-Napieralski, Vilsmeyer, and Pictet-Spengler-type reactions, and phenolic oxidative coupling have been used in the synthesis of the isomeric benzazepines. The Friedel-Crafts intramolecular acylation, so often used in the formation of six-membered heterocyclics, proved to be of less value in the synthesis of 1-benzazepines.

[2.2]Paracyclophanes, structure and dynamics

Abstract: Non-planar benzene rings, anomalous bond lengths and angles, and electronic interactions between parallel benzene nuclei are common features of the [2.2]paracyclophane system. This progress report reviews the unusual physical and, in particular, spectroscopic properties of such a strained molecular structure. Chirally substituted [2.2]paracyclophanes offer parallels to the stereochemistry of the metallocenes. Characteristics of the chemical behaviour of [2.2]paracyclophanes and analogous compounds comprise: transannular directing effects in electrophilic substitution, neighboring-group effects of the [2.2]paracyclophanyl moiety, cis-addition at the aliphatic bridges, dynamic intramolecular processes such as isomerization and racemization, and photochemical reactions.