Search results for "Reaction"
showing 10 items of 6134 documents
Chemisorption of hydrogen on charged vanadium clusters
1996
Abstract The chemisorption of hydrogen on positively charged vanadium clusters, V n + ( n = 1–17), was studied by measuring reaction rates and saturation coverages. Vanadium clusters are produced by laser vaporization and are injected into a Penning trap. Rates of the reaction V n + +H 2 → V n + H 2 are measured by axial ejection of all ions out of the trap after variable storage times and subsequent time-of-flight detection. An odd-even effect of the reaction rate is observed with odd clusters being more reactive. Clusters with low reactivity are found to be highly stable, as reflected by the respective separation energies of atoms. The number of adsorbed hydrogen atoms, m , is determined …
Reaktionen an Aluminiumoxiden. 1. Mitt.: Umsetzungen von Aceton an Aluminiumoxiden
1972
Die Umsetzungsraten von Aceton (1) an verschiedenen Aluminiumoxiden wurden bei unterschiedlichen Bedingungen untersucht. Die auftretenden Stoffe wurden durch Vergleichssubstanzen identifiziert und durch Dunnschicht- und Gas-Flussig-Chromatographie nachgewiesen. Reactions on Aluminium Oxides The reaction rates of 1 on various aluminium oxides were investigated under different conditions. The resulting products were identified comparing with synthesized compounds and by thin layer and gas liquid chromatography.
ChemInform Abstract: Oxidative Transformation of Aryls Using Molybdenum Pentachloride
2012
Molybdenum pentachloride combines a strong Lewis acid character with an unusually high oxidation potential creating a powerful reagent for oxidative transformations. Since the oxidative coupling reaction of aryls is induced at an extraordinarily high reaction rate, a variety of labile groups, e.g. iodo, tert-alkyl, etc., are tolerated on the aromatic core. Furthermore, the co-formed molybdenum salts can either be exploited for template effects to obtain uncommon geometries in a preferred manner, or redox-play starts after aqueous workup. Therefore MoCl5 represents a unique and easily available reagent.
A study of the mechanism of the oxidative cyclization of benzaldehyde semicarbazones induced by cupric perchlorate in acetonitrile
1995
Treatment of benzaldehyde semicarbazones 1a-i with cupric perchlorate in acetonitrile at 40 provided selectively the corresponding 1,2,4-triazolin-5-ones 2a-i. The relative rate constants for 2a-i formation were determined by the competitive method. The results obtained showed that electron-donating substituents (methyl and methoxy) increase the reaction rate, while the reverse was found for electron-withdrawing substituents (chloro and nitro group). The reactivity data are discussed on the grounds of two possible mechanisms.
Vergleichende kinetische untersuchungen über die basenkatalysierte reaktion von oligomethylen- und oligoäthylenglykolen mit phenylisocyanat
1961
Die durch Triathylamin katalysierte Reaktion von Oligomethylenglykolen und von Oligoathylenglykolen mit Phenylisocyanat in Dioxan bei 25°C wurde untersucht. Die Reaktionsgeschwindigkeit innerhalb der homologen bzw. polymerhomologen Reihe ist unter den angewandten Bedingungen unabhangig von der Kettenlange und der chemischen Struktur der Kette. The reaction of oligomethylene glycols (I) and oligooxyethylene glycols (II) with phenyl isocyanate in dioxane at 25°C. catalyzed by triethylamine was investigated. Under the applied conditions the reaction rate within the homologous and polymerhomologous series is independent of the chain length and the chemical constitution of the chain.
Rates of Reactions
1986
Inspite of the fact that many organotitanium compounds are well characterized, the number of kinetic studies is limited. This chapter deals primarily with such efforts directed toward elucidating the intricacies of carbonyl addition of CH3Ti(OCHMe2)3. Various other kinetic processes are also briefly discussed (Section 4.2).
Ab initiostudy of the mechanism of the atmospheric reaction: NO2+ O3→ NO3+ O2
2003
The atmospheric reaction NO2 + O3 --> NO3 + O2 (1) has been investigated theoretically by using the MP2, G2, G2Q, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. The results show that the reaction pathway can be divided in two different parts at the MP2 level of theory. At this level, the mechanism proceeds along two transition states (TS1 and TS2) separated by an intermediate, designated as A. However, when the single-reference higher correlated QCISD methodology has been employed, the minimum A and the transition state TS2 are not found on the hypersurface of potential energy, which confirms a direct reaction mechanism. Single-reference high correlated and mu…
Fundamentals of photocatalysis: The role of the photocatalysts in heterogeneous photo-assisted reactions
2021
Abstract This chapter provides some general definitions of heterogeneous photocatalysis and evaluates its performance, which is influenced by the parameters most closely related to the properties of the solid material that acts as a photocatalyst. It also discusses aspects of heterogeneous photocatalytic reactions and explains the properties that influence photoactivity. Finally, the chapter examines thermodynamic and kinetic features, including mechanistic details and parameters to define the reaction rate and correlates them to the effects of the interaction of light with the photocatalyst surface and adsorption-desorption of species involved in heterogeneous photo-assisted reactions.
The endpoint of the rp-process
1997
Abstract The endpoint of rp-process nucleosynthesis in X-ray bursts determines the fuel consumption, the energy generation, and the abundance pattern of the produced nuclei. To investigate the time structure of rp-process nucleosynthesis, we used a nuclear reaction network including nuclei from H to Sn. We found that if 2p-capture reactions are included, the synthesis of nuclei heavier than Kr proceeds faster than previously thought. Therefore, in most X-ray bursts large amounts of nuclei in the A=80–100 region are expected to be produced. With an escape factor of about 1%, X-ray bursts could account for the large observed solar system abundances of the light p-nuclei like 92 Mo and 96 Ru t…
Understanding the mechanism of polar Diels–Alder reactions
2009
A good correlation between the activation energy and the polar character of Diels-Alder reactions measured as the charge transfer at the transition state structure has been found. This electronic parameter controls the reaction rate to an even greater extent than other recognized structural features. The proposed polar mechanism, which is characterized by the electrophilic/nucleophilic interactions at the transition state structure, can be easily predicted by analyzing the electrophilicity/nucleophilicity indices defined within the conceptual density functional theory. Due to the significance of the polarity of the reaction, Diels-Alder reactions should be classified as non-polar (N), polar…