Search results for "Rate constant"
showing 10 items of 224 documents
The nucleophilicity n index in organic chemistry
2011
The nucleophilicity N index (J. Org. Chem. 2008, 73, 4615), the inverse of the electrophilicity, 1/ω, and the recently proposed inverse of the electrodonating power, 1/ω⁻, (J. Org. Chem. 2010, 75, 4957) have been checked toward (i) a series of single 5-substituted indoles for which rate constants are available, (ii) a series of para-substituted phenols, and for (iii) a series of 2,5-disubstituted bicyclic[2.2.1]hepta-2,5-dienes which display concurrently electrophilic and nucleophilic behaviors. While all considered indices account well for the nucleophilic behavior of organic molecules having a single substitution, the nucleophilicity N index works better for more complex molecules. Unlike…
The influence of aluminium cations on electrocarboxylation processes in undivided cells with Al sacrificial anodes
2005
Abstract The influence of Al cations on the electrochemical carboxylation of acenaphthylene ( 1 ), benzophenone ( 2 ), 6-methoxy-2-acetonaphthone ( 3 ), and benzyl chloride ( 4 ) has been investigated in dimethylformamide at a glassy carbon cathode. The Al 3+ ions were either added at the beginning of the experiment or were released from the anode during electrocarboxylation. It has been found that when Al cations are added to the reaction medium, they strongly influence the reduction process, in most cases leading to a complete change of the mechanism. For example, in the case of 1 , the radical anion ( 1 − ) formed upon 1e − reduction rapidly reacts with Al 3+ to give an Al(III) adduct, w…
Huge Quantum Symmetry Effect in the O + O2 Exchange Reaction.
2015
We report extensive, full quantum-mechanical calculations for the (16)O + (16)O(16)O → (16)O(16)O + (16)O collisions, for both inelastic and atom exchange processes, using a time-independent method based on hyperspherical coordinates. The rates obtained in the present study are much larger than the previously reported ones for this system. The discrepancy is attributed to a huge symmetry effect that was missing in the studies so far. This effect differs from the well-known isotope effect. Importance of this quantum effect is further confirmed by comparison with results for the (16)O + (18)O(18)O → (16)O(18)O + (18)O, exchange reaction.
Dissociation energies of silver clusters Agn+, n=14, 15, 16, 18
2003
A recently developed method to determine dissociation energies has been applied to positively charged silver clusters of size n=14, 15, 16 and 18. The method uses a combination of sequential and single step decays. It requires an uncalibrated thermometer which here is provided by the evaporation rate constants of the product clusters. For this purpose, earlier measurements [J. Chem. Phys. 57 (1998) 2786] are reanalyzed with the new method. The resulting dissociation energies are compared with the liquid drop values and the measured decay rate constants with expected rate constants from detailed balance theory.
Ein modell zur beschreibung bimolekularer reaktionen zwischen reaktiven gruppen, die in zwei polymerknäuel eingebaut sind
1968
Die Beobachtung, das die Geschwindigkeitskonstante des Kettenabbruchs bel der radikalischen Polymerisation des Methylmethacrylats umgekehrt proportional der Viskositat des Losungsmittels und vollig unabhangig vom Molekulargewicht ist, wird durch folgendes Modell erklart: 1. Die Polymerknauel behindern nicht ihre gegenseitigen Bewegungen und konnen sich bei einer Begegnung vollstandig durchdringen (Unabhangigkeit der Selbstdiffusionskonstante von der Konzentration). 2. Die Reaktion findet im Uberlappungsraum zweier sich begegnender Polymerradikale wahrend der Begegnungsdauer τ statt. Eine statistische Rechnung zeigt, das unter dieser Annahme die gemessene bimolekulare Geschwindigkeitskonstan…
Kinetics of the formation reactions of trichloro- and tribromomethyl hypohalites and alcohols in the gas-phase: Theoretical study
2007
Abstract The CX3OY molecules (X = Cl, Br and Y = H, F, Cl, Br) can be formed in the atmosphere by the recombination CX3 + OY and CX3O + Y reactions. In the present study the results of a theoretical analysis of the kinetics and thermochemistry of this class of reactions are performed. The molecular properties of the reactants and products were derived from ab initio calculations. The high-pressure limiting rate constants for the recombination reactions were evaluated using a version of the statistical adiabatic channel model. The kinetic equations derived in this study allow a description of the kinetics of the reactions under investigation in the temperature range of 200–400 K.
The influence of internal degrees of freedom on the unimolecular decay of the molecule–cluster compound Au8+CH3OH
2002
Time-resolved photodissociation measurements of the sequential reaction Au8+CH3OH→Au8+→Au7+ and the direct reaction Au8+→Au7+ have been performed for several excitation energies. The production rates and yields of the final state Au7+ in the sequential process are strongly influenced by the excitation energy deposited into the evaporated methanol molecule during the initial fragmentation step. Both the rate constants and yields can be fitted with a single parameter, the cluster–methanol binding energy.
Quantum Dynamics of the 18O + 36O2 Collision Process
2015
We report full quantum cross sections and rate constants for the (18)O + (36)O2 → (36)O2 + (18)O collision process. This constitutes to the best of our knowledge the first dynamical study of the (18)O(18)O(18)O system, with three identical (18)O oxygen atoms. We emphasize the comparison with the (16)O + (32)O2 collision as this latter presents the exact same features as the one treated here, except the consistent change of mass for all three atoms. We find very similar behaviors in the cross sections, and we confirm that the rates are faster when three identical nuclei are involved. In particular, we cannot dynamically study this system with classical trajectory methods, and we have to incl…
Facile approaches to build ordered amphiphilic tris(phthalocyaninato) europium triple-decker complex thin films and their comparative performances in…
2010
Solution processed thin films of an amphiphilic tris(phthalocyaninato) rare earth triple-decker complex, Eu(2)[Pc(15C5)(4)](2)[Pc(OC(10)H(21))(8)], have been prepared from three different methods: self-assembly (SA) annealed in solvent vapor, quasi-Langmuir-Shäfer (QLS) and drop casting methods. In particular, we successfully developed a simple QLS process for fabricating ordered multilayers with a good thickness control. The films prepared from three different methods were characterized by a wide range of methods including electronic absorption spectra, IR, X-ray diffraction, atomic force microscopy (AFM), and current-voltage (I-V) measurements. J-type aggregates have been formed with the …
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.