Search results for "Reaction"

1987

Die radikalinduzierte polymerisation von acrolein und α-methylacrolein in dimethylformamid. Polymere acroleine. 22. Mitt.1

1962

Die Polymerisation von Acrolein in Dimethylformamid (DMF) bei 40 und 50°C mit wechselnden Mengen Azodiisobuttersaurenitril wird beschrieben. Bei Umsatzen uber 16% tritt unter diesen Bedingungen Gelbildung ein. Methacrolein wurde mit verschiedenen Katalysatoren in DMF polymerisiert. Die Polymerisate bleiben bis zu hohen Umsatzen in Losung. Die Bruttoaktivierungsenergie ergibt sich zu 21 kcal/Mol. Die Bruttogeschwindigkeit als Funktion der Monomeren-Konzentration und der Konzentration von Azodiisobuttersaurenitril last sich bei 50°C durch folgende Gleichung beschreiben: The polymerization of acrolein in DMF at 40 and 50°C. in presence of varying amounts of azodiisobutyronitrile was investigat…

Understanding the Participation of Quadricyclane as Nucleophile in Polar [2σ + 2σ + 2π] Cycloadditions toward Electrophilic π Molecules

2008

The formal [2sigma + 2sigma + 2pi] cycloaddition of quadricyclane, 1, with dimethyl azodicarboxylate, 2, in water has been studied using DFT methods at the B3LYP/6-31G** and MPWB1K/6-31G** levels. In the gas phase, the reaction of 1 with 2 has a two-stage mechanism with a large polar character and an activation barrier of 23.2 kcal/mol. Inclusion of water through a combined discrete-continuum model changes the mechanism to a two-step model where the first nucleophilic attack of 1 to 2 is the rate-limiting step with an activation barrier of 14.7 kcal/mol. Analysis of the electronic structure of the transition state structures points out the large zwitterionic character of these species. A DF…

1987

Approach Matters : The Kinetics of Interfacial Inverse-Electron Demand Diels-Alder Reactions

2017

Rapid and quantitative click functionalization of surfaces remains an interesting challenge in surface chemistry. In this regard, inverse electron demand Diels Alder (IEDDA) reactions represent a promising metal-free candidate. Herein, we reveal quantitative surface functionalization within 15 min. Furthermore, we report the comprehensive effects of substrate stereochemistry, surrounding microenvironment and substrate order on the reaction kinetics as obtained via a combination of XPS and surface-bound mass spectrometry (DART-MS).

Coadsorption of NRR and HER Intermediates Determines the Performance of Ru-N4 toward Electrocatalytic N2 Reduction

2021

Efficiency of the electrochemical N2 reduction reaction (NRR) to ammonia is seriously limited by the competing hydrogen evolution reaction (HER) but our current atomic-scale insight on the factors controlling HER/NRR competition are unknown. Herein we unveil the elementary mechanism, thermodynamics, and kinetics determining the HER/NRR selectivity on the state-of-the-art NRR electrocatalyst, Ru-N4 using constant potential density functional theory calculations (DFT). The calculations show that NRR and HER intermediates coadsorb on the catalyst where HER is greatly suppressed by the NRR intermediates. The first reaction step leading to either *NNH or *H determines the selectivity towards NRR…

A Lotka-type model for oscillations in surface reactions

1997

In this paper we introduce a reaction model on a lattice which leads to oscillations. The model consists of two monomolecular and one bimolecular reaction step and is related to the Lotka model. Despite the simple evolution rules, the model shows a complex behaviour (i.e. the appearance of oscillations). This offers us the opportunity to test different types of stochastic approximations and compare them with the results of a Monte Carlo simulation. The simulation is performed on a large lattice (L = 1024) in order to take long-range correlations into account. Comparing the results of this simulation with the stochastic approaches shows that only advanced numerical approximations are able to…

Recent Advances in Charge-Accelerated aza-Claisen Rearrangements

2005

Aza-Claisen rearrangements (3-aza-Cope rearrangements) have gained an in- creasing interest in synthetic organic chemistry. Originally, the exceptionally high reaction temperatures of this hetero variant of the well-known 3,3-sigmatropic reaction limited their applicability to selected molecules. Since about 1970, charge acceleration enabled a signifi- cant reduction of the reaction temperature to be achieved, and cation- and anion-promoted rearrangements found their way into the syntheses of more complex molecules. The first to- tal syntheses of natural products were reported. The development of zwitterionic aza-Claisen rearrangements allowed the reactions to be run at room temperature or …

Reakcijas laiku testēšanas rīka izveide cilvēka uztveres testēšanai

2022

Reakcijas laiks ir ilgi pētīts kognitīvās zinātnes temats. Tas ir pamats daudz plašākiem pētījumiem vairākās nozarēs, kas izskaidro tā popularitāti. Tehnoloģijas attīstības laikā, reakcijas laika pētīšana ir kļuvusi daudz ērtāk pētāma lieta, bet tas arī ir radījis vairākas problēmas, jo daudzi pētījumi nav ņēmuši vērā programmatūras un aparatūras aiztveri. Tāpēc ir svarīgi izveidot savu rīku, lai no tā izvairītos.

The relationship between motor timing, reaction time and academic achievements in primary school children.

2017

Aim: Recent studies have reported a correlation between motor skills and school performance, which is different according to the type of motor ability or academic subject examined (Fernandes et al, 2016; Bellafiore et al., 2016). The aim of this study was to analyze the relationship between motor timing, reaction time and achievements in mathematics and Italian in sedentary and active children. Methods: Seventy-eight children (8.55±1.43 years old, 28.93±5.74 kg weight, 126.54±4.74 cm height and 19.30±2.62 kg/m2 BMI) were randomly recruited by a primary school of Palermo, 68% of them practiced a sport outside the academic hours. The motor timing was measured with the finger and foot tapping …