Search results for "Anion"

1990

The effect of lithium tert-butoxide (t-BuOLi) on rate constants and equilibrium constants of reactions involved in the initial stage of the anionic polymerization of methyl methacrylate (MMA) in tetrahydrofuran, initiated by methyl α-lithioisobutyrate (P) was investigated at 23 ± 3°C. Addition of t-BuOLi decreases the rate constants of initiation and propagation by one order of magnitude; the rate constants of termination by cyclization decrease by two orders of magnitude. This leads to an overall tenfold higher preference of propagation with respect to termination and explains the favourable effect of alkoxide in the polymerization reported earlier. Within experimental error, the equilibri…

Anionische Polymerisation in Schwach Solvatisierenden Lösungsmitteln

2007

The anionic polymerization of styrene initiated by cumylsodium and carried out in cumyl methyl ether has been examined with use of conversion kinetics and molecular weight distribution. The solvent has a weaker solvation power than THF and THP, which have been studied with the same experimental technique. The polymerization rate is first order relative to monomer and the rate constant has a value of ca. 1 mole−1 1. sec.−1 at − 20.5°C. The constant is only slightly dependent on the initiator concentration, but the molecular weight distribution is broader than a Poisson function. Added electrolyte has little effect on the propagation constant but it greatly alters the molecular weight distrib…

Über die wirksamkeit von lewis-basen als initiatoren der anionischen polymerisation von formaldehyd. 27. Mitt. über polyoxymethylene

1966

Die anionische Polymerisation des monomeren Formaldehydes mit LEWIS-Basen wurde bei −78°C in Ather, Aceton und Toluol untersucht. Die Basizitat der LEWIS-Basen ist ein wichtiger Faktor for ihre Initiatoraktivitat, ist jedoch nicht allein entscheidend; es spielen auch strukturelle und steren rische Faktoren eine Rolle. Primare Amine sind wahrscheinlich deshalb schlechte Initiatoren, weil sie mit Formaldehyd Methylol- und Dimethylolamine bilden. Verzweigungen aliphatischer Substituenten wirken sich um so starker retardierend aus, je naher sich die Verzweigungsstelle am Stickstoffatom befindet. Die Polymerisationsgeschwindigkeit steigt bei den meisten Aminen mit zunehmender Polaritat des Losun…

ChemInform Abstract: Heterocycles from α-Aminonitriles

2014

Owing to their various modes of reactivity, α-aminonitriles represent versatile building blocks for the construction of a wide range of nitrogen heterocycles. The present Concept article focuses on synthetic methodologies using their bifunctional nature which is the basis of their reactivity as α-amino carbanions and as iminium ions. Reactions exclusively taking place on either the amine or on the nitrile moiety will not be considered.

Nucleophilic Additions of the Cyanide Anion to 4,4-Dichloro-1,1-Diphenyl-2-Azabuta-1,3-Diene

2002

The unexpected formation of a 2H-pyrrole by reaction of potassium cyanide with 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene and the mechanism of this reaction are described and the structures of the product and a trapped intermediate confirmed by X-ray crystallographic studies.

Oxyanion Holes and Their Mimics

2009

Phosphororganische Verbindungen. 60. Mitt. Aufbau und Eigenschaften eines optisch aktiven Anionenaustauschers mit identischem Chiralitäts- und Ladung…

1968

Chlormethyliertes Polystyrol (vernetzt mit 0,5% Divinylbenzol) wird mit (+)-Methyl- n-propyl-phenyl-phosphin quartarisiert. Der entstehende Austauscher besitzt eine Kapazitat von 2,68 mVal/g. Mandelsaure, Atrolactinsaure und Traubensaure konnten an diesem Material nicht in die Antipoden gespalten werden. Chlormethylated polystyrene (crosslinked with 0.5% divinylbenzene) is quaternized with (+)-methyl-n-propyl-phenyl-phosphine. The resultant anion exchanger has a capacity of 2.68 m.equiv./g. Mandelic acid, atrolactic, and rac. tartaric acid could not be resolved into the antipodes on this material.

Maturation of a Key Resource – The Germanium-68/Gallium-68 Generator: Development and New Insights

2011

(68)Ge/(68)Ga radionuclide generators have been investigated for almost fifty years, since the cyclotron-independent availability of positron emitting (68)Ga via the (68)Ge/(68)Ga system had always attracted researches working in basic nuclear chemistry as well as radiopharmaceutical chemistry. However, it took decades and generations of research (and researchers) to finally reach a level of (68)Ge/(68)Ga radionuclide generator designs adequate to the modern requirements of radiometal labelling chemistry. Nevertheless, most of the existing commercial generator systems address aspects of (68)Ge breakthrough and safe synthesis of (68)Ga radiopharmaceuticals by adopting eluate post-processing …

Chloride ligands on DNA-stabilized silver nanoclusters

2023

DNA-stabilized silver nanoclusters (AgN-DNAs) are known to have one or two DNA oligomer ligands per nanocluster. Here, we present the first evidence that AgN-DNA species can possess additional chloride ligands that lead to increased stability in biologically relevant concentrations of chloride. Mass spectrometry of five chromatographically isolated near-infrared (NIR)-emissive AgN-DNA species with previously reported X-ray crystal structures determines their molecular formulas to be (DNA)2[Ag16Cl2]8+. Chloride ligands can be exchanged for bromides, which red-shift the optical spectra of these emitters. Density functional theory (DFT) calculations of the 6-electron nanocluster show that the …

Stabilisation of Exotic Tribromide (Br3−) Anions via Supramolecular Interaction with A Tosylated Macrocyclic Pyridinophane. A Serendipitous Case.

2020

Tetraaza-macrocyclic pyridinophane L-Ts, decorated with a p-toluenesulfonyl (tosyl