Search results for "Reaction"

Ultradian rhythms in avoidance behavior of DBA mice

1994

This study investigates ultradian rhythm in avoidance behavior of mice, which may constitute a basic rest activity cycle (BRAC). Reaction times (RTs) of an avoidance response to a visual warning stimulus that preceded an electric shock were measured by the use of a computer-controlled shuttle box. The male naive DBA mice were brought to a criterion of 98% correct responses in numerous training sessions. For each subject, all the temporal sequences of the RTs in the trials following achievement of the criterion were examined with discrete Fourier transform. Periodograms were obtained from three sessions for each of the two animals in the first experiment and from 15 subjects in the second ex…

Phase Equilibrium for the Esterification Reaction of Acetic Acid + Butan-1-ol at 101.3 kPa

2007

In this work, the thermodynamic behavior of catalytic esterification reaction equilibrium and vapor–liquid equilibria (VLE) for the quaternary reactive system acetic acid + butan-1-ol + butyl acetate + water and constituent binary systems acetic acid + butyl acetate, butan-1-ol + butyl acetate, and butan-1-ol + water have been determined at 101.3 kPa, and liquid–liquid equilibria (LLE) of the binary system butan-1-ol + water have also been determined. The esterification reaction rate of the acetic acid and butan-1-ol mixture is very slow. So, in this study, p-toluenesulfonic acid was selected as the catalyst to accelerate the chemical reaction. The measured VLE data were correlated by the N…

Preparation of 5-methyl-2-sulfanyl-7h-1,3,4-thiadiazolo[3,2-a]-pyrimidin-7-ones

2007

7H-1,3,4-Thiadiazolo[3,2-a]pyrimidin-7-ones can be prepared by the acylation of 5-amino-1,3,4-thiadiazoles with diketene and subsequent ring closure (dehydration). Whereas arylthio substituents (SC6H5) can be introduced in 2-position by the replacement of Br, alkylthio groups (SC2H5) have to be already presentin the starting 5-amino-1,3,4-thiadiazole. The ambident nucleophile 2-thiazolidinethione reacts in the Br substitution reaction on the N atom.

Die Herstellung einer molekulareinheitlichen Tri-, Tetra- und Pentamethacrylsäure. V. Mitt. Modelle für Matrizenreaktionen

1968

Vom p-Kresol sowie einer phenolischen Zwei- und einer Dreikernverbindung wurden mit verschiedenen Acylierungsmethoden Methacrylsaureester erhalten; die Zweikernverbindung enthielt danach zwei und die Dreikernverbindung drei Methacrylreste. Loste man diese Methacrylsuureester in groser Verdunnung in siedendem Benzol und lies gleichzeitig einen grosen Uberschus an Radikalen aus α.α′-Azoisobuttersauredinitril einwirken, so wurde beim Methacrylsaure-p-kresylester eine Polymerisation unterdruckt. Bei den mehrfachen Estern der Mehrkernverbindungen wurde die polyrmerisationsahnliche Additionsreaktion auf die einzelnen Molekule begrenzt (intramolckulare Polymerisation); sie ergab neben einer cyclis…

Ein neuer weg zur herstellung von oligomeren aus acryl- und vinylverbindungen; modell einer matrizenreaktion

1966

In einer Reihe vorangehender Untersuchungen wurde die Herstellung molekulareinheitlicher, phenolischer Mehrkernverbindungen beschrieben. Sie besitzen je Phenolbaustein eine phenolische Hydroxylgruppe, wie systematisch untersuchte Acylierungen sowie Methylierung und Arylierung dieser Mehrkernverbindungen zeigen. In der vorliegenden Mitteilung wurde bei einer Zwei- und Dreikernverbindung an den phenolischen Hydroxylgruppen mit Acrylsaurechlorid umgesetzt, so das die entstandenen Verbindungen so viele polymerisationsfahige Reste wie phenolische Bausteine besasen. Die Polymerisation der Acrylsaurederivate in sehr groser Verdunnung gab oligomere Leiterverbindungen, die durch alkalische Hydrolyse…

Cure behaviour of epoxy resin matrices for carbon fibre composites

1999

The cure behaviour of two resin formulations (with high and low curing agent content respectively) of an epoxy resin system, used as matrix for carbon fibre composites, was studied through calorimetric analysis. The aim of this work is to investigate the kinetics of this specific epoxy system in order to be able to choose a proper set of processing parameters which will give good composite material properties. The shape of the conversion curves gives evidence of the differences in the cure kinetics of the two systems. Furthermore, the values of the activation energies were determined both for formulation in the conversion range where vitrification occurs, following a phenomenological approa…

The identification of vicinally substituted cyclohexane isomers in their mixtures by 1H and 13C NMR spectroscopy.

2000

The radical addition reactions of organobromine compounds, XBr (X = CH2COOMe, PhCH2, CHBr2 and CCl3) with cyclohexene afforded mixtures of cis/trans isomer pairs of 1-X-2-Br-cyclohexanes. In addition to benzyl benzoyloxy derivatives are formed also, when benzoyl peroxide is used as an initiator. Owing to the great difficulties in separating these cis/trans isomer pairs, they are identified directly in their mixtures by NMR spectroscopy. In addition to one-dimensional (ID) 1H, proton decoupled 13C and DEPT-135, also two-dimensional (2D) 13C-13C INADEQUATE as well as 1H-13C HMQC experiments have been used in assigning the signals of each compound in their mixtures. The identification of each …

Asymmetric Addition and Cycloaddition Reactions with Ylidene‐Five‐Membered Heterocycles

2021

Five-membered heterocycles bearing an exocyclic double bond have been successfully used as substrates in asymmetric addition and cycloaddition reactions. Ylidene-heterocycles are attractive substrates due to their high functionalization and the presence of an electrophilic conjugated exocyclic double bound that can participate in nucleophilic addition reactions as well as cycloaddition reactions, which may be triggered by the formation of aromatic intermediates or products in many cases. During the last decades, catalytic methodologies have been developed using ylidene-heterocycles as substrates in order to synthesize useful optically active heterocyclic derivatives. 4-Ylidene-pyrazol-5-one…

Enantioselective Addition of Dimethylzinc to Aldehydes Catalyzed by N-Substituted Mandelamide-Ti(IV) Complexes.

2005

Abstract Amides derived from ( S )-(+)-mandelic acid in the presence of titanium isopropoxide catalyze the enantioselective addition of dimethylzinc to aromatic aldehydes with good yields and ee up to 90%.

2014

Carbon-centered radicals represent highly useful reactive intermediates in organic synthesis. Their nucleophilic character is reflected by fast additions to electron deficient C=X double bonds as present in iminium ions or cationic heterocycles. This review covers diverse reactions of preformed or in situ-generated cationic substrates with various types of C-radicals, including alkyl, alkoxyalkyl, trifluoromethyl, aryl, acyl, carbamoyl, and alkoxycarbonyl species. Despite its high reactivity, the strong interaction of the radical’s SOMO with the LUMO of the cation frequently results in a high regioselectivity. Intra- and intermolecular processes such as the Minisci reaction, the Porta react…