Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles, 2. Comparison of the chemistry and photobehavior of the trans-dichloro- and trans-dicyano- complexes of cyclam, 1,4-C2-cyclam, and 1,11-C3-cyclam

The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,11-C3-cyclam (1,4,8,11-tetraazabicyclo[9.3.3]heptadecane) is reported. Only trans complexes are formed, and the structure of trans-[Cr(1,11-C3-cyclam)Cl2]PF6 is presented. The chemical and photophysical behavior of the 1,11-C3-cyclam complexes are compared with those of the corresponding cyclam (1,4,8,11 tetraazacyclotetradecane) and 1,4-C2-cyclam (1,4,8,11-tetraazabicyclo[10.2.2]hexadecane) complexes. The aquation rate of trans-[Cr(1,11-C3-cyclam)Cl2]+ is similar to that of the corresponding 1,4-C2-cyclam complex and is more than 5 orders of magnitude faster than the cyclam counterpart. A monotonic increase in the extinction coefficient is observed on going from the cyclam complexes to the 1,11-C3-cyclam complexes to the 1,4-C2-cyclam complexes, and this is related to the degree of centrosymmetry in each complex. The trans-[Cr(1,11-C3-cyclam)(CN)2]+ complex is a weak emitter in aqueous solution with a room-temperature emission maximum at 724 nm (tau=23 micros). Like the corresponding 1,4-C2-cyclam complex (tau=0.24 micros), the 1,11-C3-cyclam complex shows no deuterium-isotope effect in room-temperature solution. This is in marked contrast to the corresponding cyclam complex which has an emission lifetime of 335 micros and a significant deuterium isotope effect in room-temperature solution. Low temperature (77K) data are also presented in an attempt to understand the differences in photophysical behavior.     

The Chemistry of Methane Remediation by a Non‐thermal Atmospheric Pressure Plasma

The destruction of methane by a nonthermal plasma in atmospheric pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the endproducts are determined by online FTIR spectroscopy and the plasma chemistry is interpreted using kinetic modelling. For a deposited energy of 118 kJ m^–3, the destruction is 12% in nitrogen decreasing monotonically to 5% in air. The major endproducts are HCN and NH₃ in nitrogen and CO, CO₂, N₂O, NO and NO₂ for gas streams containing oxygen. The chemistry in pure nitrogen is predominantly due to reactions of electronicallyexcited nitrogen atoms, N(²D). The addition of oxygen converts the excited state nitrogen into nitrogen oxides reducing the methane destruction which then arises by O and OH reactions yielding CO and, to a lesser extent, CO₂. The modelling correctly predicts the magnitude of the methane destruction as a function of added oxygen and the concentrations of the endproducts for processing in both nitrogen and air.     

Separation of Ra and Th from rock matrices for alpha-spectrometry

Dating rocks using²²⁶Ra/²³⁰Th isochrons demands radiochemical purification of radium and thorium. This paper presents an improved method. Rocks are solubilised by nitric/nydrofluoric digestion followed by dissolution of insoluble fluorides by boric/nitric acids, and Th is extracted by passing the 8M nitric solution through an anion column in nitrate form. The eluant contains Ra and Ba which are precipitated as sulphate and redissolved in alkaline EDTA. Complete separation of Ba and Ra from sulphate is on an AG 1×8 anion column in EDTA form, which was found better than the chloride form. The Ba+Ra is separated on an AG 50W×8 cation column, and uses CDTA as an eluant for Ba. Careful pH control is essential. Ra elutes later with EDTA or 4M HCl and is precipitated with 125 g barium as sulphate to yield a source suitable for -spectrometry, or further treated to electroplate the Ra. The yield tracers used are²²⁸Th and²²⁴Ra. Because the sample contains natural²²⁴Ra a correction must be applied, calculated from the amount of natural²³²Th in the Th spectrum. Th may be precipitated with 100 g of ferric iron and gives a spectrometry-quality source, but further purification and electrodeposition was found to be preferable. Variations on the method for the case of analysis of calcium-rich fish otoliths are described.     

A simple and expedient method for the preparation of N-chlorohydantoins

A simple and efficient methodology for the preparation of N-chlorinated hydantoins is presented. These versatile chlorenium sources were isolated in high yield after a simple recrystallization. Among the ten examples are the first chiral N-chlorohydantoins.     

A composite chiral pair of rotational bands in the odd-A nucleus 135Nd

High-spin states in 135Nd were populated with the 110Pd(30Si,5n)135Nd reaction at a 30Si bombarding energy of 133 MeV. Two DeltaI=1 bands with close excitation energies and the same parity were observed. These bands are directly linked by DeltaI=1 and DeltaI=2 transitions. The chiral nature of these two bands is confirmed by comparison with three-dimensional tilted axis cranking calculations. This is the first observation of a three-quasiparticle chiral structure and establishes the primarily geometric nature of this phenomenon.     

The excitation of acoustic resonances by vortex shedding

A single acoustic resonance, excited by vortex shedding from the trailing edge of a flat plate, has been studied in detail. The resonance was generated in the working section of a low-speed wind tunnel and the scale was large enough for accurate measurements to be made. The trailing edge was designed so that it could be made to oscillate slightly to simulate the correlating effect of the resonance on the vortex shedding.     

Verteilung der Translationsenergie auf die Produkte von Methylradikalreaktionen

Ohne Zusammenfassung     

Charge density distributions and sigma bond inductive effects in hydrocarbons and hydrocarbon ions

Atomic orbital charge densities have been calculated for the electron systems of a number of hydrocarbon molecules, by an electronegativity equalization method. These electron distributions have been used to analyze the relative inductive effects of alkyl groups, the transmission of electronic effects through localized bonds, the inductive stabilization of simple hydrocarbon ions, and the dependence of the ¹H and ¹³C chemical shifts on the corresponding partial charges of the atoms. The charge densities calculated by electronegativity equalization were compared to those predicted by various molecular orbital methods.

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Zusammenfassung Mit Hilfe einer Methode, die auf der Angleichung von Elektronegativitäten beruht (electronegativity equalization), sind atomare Orbitalladungsdichten für -Elektronensysteme einer Reihe von Kohlenwasserstoffmolekülen berechnet worden. Die Ladungsdichten werden mit den Voraussagen verschiedener MO-Methoden verglichen.Diese Elektronenverteilungen werden zur Analyse der relativen induktiven Effekte von Alkylgruppen, der Weiterleitung elektronischer Effekte durch lokalisierte Bindungen, der induktiven Stabilisierung einfacher Kohlenwasserstoffionen und der Abhängigkeit der chemischen Verschiebung von ¹H und ¹³C von den partiellen Ladungen der Atome benutzt.

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Résumé Les densités de charge dans les orbitales atomiques ont été calculées pour les systèmes d'électrons d'un certain nombre de molécules d'hydrocarbure à l'aide d'une méthode d'égalisation des électronégativités. Ces distributions électroniques ont été utilisées pour analyser les effects inductifs relatifs des groupements alkyles, la transmission des effets électroniques à travers les liaisons localisées, la stabilisation par effet inductif des ions hydrocarbures simples, et la relation entre les déplacements chimiques de ¹H et ¹³C et les charges atomiques partielles correspondantes. Les densités de charges calculées ici ont été comparées à celles obtenues par différentes méthodes d'orbitales moléculaires.