Ten‐vertex rhodadithiaborane ­chemistry: [8‐{I(CH2)5}‐3‐(η5‐C5Me5)‐arachno‐3,7,8‐RhS2B8H9]

Neutral 8‐(5‐iodo‐n‐pentyl)‐3‐(η⁵‐penta­methyl­cyclo­pentadi­enyl)‐arachno‐3‐rhoda‐7,8‐di­thia­undecaborane, [Rh(C₅H₁₉B₈­IS₂)­(C₁₀H₁₅)], obtained from the [arachno‐7,8‐S₂B₉H₁₀]^? anion by treatment with I(CH₂)₅I followed by [Rh(C₅Me₅)Cl₂]₂ and N,N,N′,N′‐tetra­methyl‐1,8‐di­amino­naphthalene, has the 11‐vertex cluster geometry of [arachno‐7,8‐S₂B₉H₁₀]^?, but with an {Rh(C₅Me₅)} unit in the 3‐position instead of a {BH} unit, and with a –(CH₂)₅I chain attached exo to an S atom.     

4′‐Vinyl‐2,2′:6′,2′′‐ter­pyridine

The title compound, C₁₇H₁₃N₃, is a versatile precursor for polymeric ter­pyridine derivatives and their metal complexes. The mol­ecule has transoid and near‐coplanar pyridine rings. However, the vinyl group is forced out of the plane of the terpyridyl moiety by a close H?H contact.     

Block Copolypeptides Prepared by N‐Carboxyanhydride Ring‐Opening Polymerization

N‐Carboxyanhydride ring‐opening polymerization (NCA ROP) is a synthetically straightforward methodology to generate homopolypeptides. Extensive control over the polymerization permits the production of highly monodisperse synthetic polypeptides to a targeted molecular weight in the absence of unfavorable side reactions. Sequential NCA ROP permits the creation of block copolypeptides composed of individual polypeptide blocks boasting different functionalities, secondary structures, and desirable chemical properties. Consequently, a plethora of novel materials have been generated that have found wide‐range applicability. This review offers an insight into contemporary synthetic approaches toward NCA ROP before highlighting a number of block copolypeptide architectures generated.     

Capacitance and Structure of Electric Double Layers: Comparing Brownian Dynamics and Classical Density Functional Theory

Journal of Solution Chemistry - We present a study of the structure and differential capacitance of electric double layers of aqueous electrolytes. We consider electric double layer capacitors...     

Infrared Spectra of trans-nitrobis (2, 4-pentanediono) Aniline-Cobalt(III) Complexes

The infrared spectra of eighteen complexes of general formula trans-[Co(NO₂) (acac)₂ (R-C₆H₄NH₂)] (acac = acetylacetonate anion, R = 3- or 4-aniline substituent) are discussed. ¹⁵N-Labelling of the complexes containing aniline and p-toluidine yields assignments of the N-H, C-N and Co-N stretching frequencies and the N-H bending frequencies. These assignments receive support from the observed frequency shifts induced by varying the substituent R which also permits the assignment of the Co-o stretching frequencies.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Spectrophotometric study of the cobalt-3-nitroso-2,6-pyridinediol reaction

Summary A spectrophotometric study has been made on the cobalt-3-nitroso-2, 6-pyridinediol reaction. The yellow complex formed has an absorption maximum at 411 nm and a molar absorptivity of 3.4·10⁴ l mole^–1 cm^–1. The system follows Beer's law.

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Zusammenfassung Die Reaktion zwischen Kobalt und 3-Nitroso-2,6-Pyridindiol wurde spektrophotometrisch untersucht. Die maximale Absorption des sich bildenden gelben Komplexes liegt bei 411 nm, seine molare Extinktion beträgt 3,4·10⁴ l Mol^–1 cm^–1. Die Farbreaktion entspricht dem Beerschen Gesetz.

     

Kinetics and mechanism of the benzoin isobutyl ether photoinitiated polymerization of styrene

The kinetics of the photopolymerization of styrene in bulk and in dilute systems in the presence of benzoin isobutyl ether as photoinitiator have been examined. The values of the intensity exponent, calculated at different temperatures or at different styrene concentrations, and the monomer exponent, calculated at various intensities, showed significant departure from those predicted by the ideal kinetic scheme, particularly at high intensity, at low temperature, or at low styrene concentrations. Low molecular weight polymer was the dominant product when high light intensity or low polymerization temperature was used. As the temperature was raised, however, or as the intensity was reduced, a high molecular weight polymer became progressively more important. Kinetic and molecular weight data suggest that at low temperature, high intensity, and/or at low monomer concentration, the benzoyl radical is the dominant initiating species; and the benzyl ether radical was consumed mainly in the termination step. At low intensity, high temperature and/or high monomer concentration, however, it appears that both benzoyl and benzyl ether radicals initiated polymerization.     

π-Interaction in metal Β-ketoenolates

The available data (supplemented where necessary) on the electronic, nuclear magnetic resonance and vibrational spectra of metal -ketoenolates has been analysed to assess the relative contributions of donor and acceptor metal-ligand -bonding in the first transition period metal (III) -ketoenolates. The effects of the metal ion and the ligand substituent on the -interaction in the -ketoenolate ring are discussed in terms of established theoretical concepts.

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Zusammenfassung Die bekannten Daten (ergÄnzt, falls notwendig) der elektronischen und kernmagnetischen Resonanz sowie der Schwingungsspektren von Metall--ketoenolaten wurden analysiert, um die relativen BeitrÄge von Donor- und Akzeptor (Metall-Ligand) -Bindung in Metall(III)ketoenoIaten der ersten übergangsperiode zu ermitteln. Die Einwirkung des Metallions und des Ligandsubstituenten auf die -Bindung im -Ketoenolatring werden diskutiert auf der Grundlage von bekannten theoretischen Prinzipien.

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Résumé L'examen des résultats antérieurement publiés (supplementés ou nécessaire) des spectres électroniques, résonance nucléaire magnétiques et vibrationnel nous a amenés à préciser les contributions relatifs de liaison- donneur et accepteur entre métal et ligand de la première période transitionelle métal(III) -kétoénolates. Les effects de l'ion métallique et du ligand substituent exercés sur l'interaction- dans le noyau -kétoénolate sont discutés selon les idées théoriques déjà établies.

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This work was supported by University of Cape Town and C.S.I.R. Research Grants. We thank the National Institute for Metallurgy for a bursary (to R.D.H.).