Search results for "Reactivity"
showing 10 items of 880 documents
A theoretical study on the regioselectivity of 1,3-dipolar cycloadditions using dft-based reactivity indexes
2004
The regioselectivity for a series of four 1,3-dipolar cycloaddition reactions has been studied using global and local reactivity indexes. The results of the theoretical analysis suggest that for asynchronous cycloadditions associated to polar processes, the regioselectivity is consistently explained by the most favorable two-center interactions between the highest nucleophilic and electrophilic sites of the reagents.
Avoidant coping style and verbal-cardiovascular response dissociation
1996
Abstract This study explored the relationship between an avoidant coping style and three responses during three experimental periods (i.e., speech preparation, speech delivery, and recovery). One response was cardiovascular reactivity, the two other responses were subjective in nature: self-reports of anxiety and self-estimations of blood pressure. Subjects were 20 male and 20 female students who scored either in the upper third (i.e., high-avoiders) or lower third (i.e., low-avoiders) on cognitive avoidance (Krohne, 1989). When compared to subjects scoring low on avoidance, those high on avoidance showed greater systolic blood pressure (SBP) reactivity and evidenced verbal-autonomic respon…
Measuring Public Speaking Anxiety: Self-report, behavioral, and physiological
2021
Self-reports are typically used to assess public speaking anxiety. In this study, we examined whether self-report, observer report, and behavioral and physiological reactivity were associated with each other during a speech challenge task. A total of 95 university students completed a self-report measure of public speaking anxiety before and after the speech challenge. Speech duration (i.e., behavioral measure), physiological reactivity, as well as speech performance evaluated by the participants and observers were also recorded. The results suggest that self-reported public speaking anxiety predicts speech duration, as well as speech quality, as rated by the participants themselves and ob…
About the selectivity and reactivity of active nickel electrodes in C–C coupling reactions
2020
Active anodes which are operating in highly stable protic media such as 1,1,1,3,3,3-hexafluoroisopropanol are rare. Nickel forms, within this unique solvent, a non-sacrificial active anode at constant current conditions, which is superior to the reported powerful molybdenum system. The reactivity for dehydrogenative coupling reactions of this novel active anode increases when the electrolyte is not stirred during electrolysis. Besides the aryl-aryl coupling, a dehydrogenative arylation reaction of benzylic nitriles was found while stirring the mixture providing quick access to synthetically useful building blocks.
A molecular electron density theory study of the chemo- and regioselective [3 + 2] cycloaddition reactions between trifluoroacetonitrile N-oxide and …
2018
Abstract The [3 + 2] cycloaddition (32CA) reaction between trifluoroacetonitrile N-oxide (NO 7) and 2,2,4,4-tetramethyl-3-thioxocyclobutan-1-one (THK 12) as well as the self-dimerization of NO 7 as a competitive pathway were studied within the Molecular Electron Density Theory (MEDT) using several DFT functionals together with def2-TZVP basis set. Taking CCSD(T)/TZVP activation energies as reference, among the employed functionals, just the B2PLYP-D3(BJ) one is able to portray complete predominance of 32CA reaction over self-dimerization process in excellent agreement with the experimental outcomes. Analysis of the global reactivity indices permits to characterize NO 7 and THK 12 as a stron…
Unveiling the Reactivity of Cyclic Azomethine Ylides in [3+2] Cycloaddition Reactions within the Molecular Electron Density Theory
2020
A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitrones with ketenes.
2017
The [3 + 2] cycloaddition (32CA) reaction between nitrones and ketenes has been studied within the Molecular Electron Density Theory (MEDT) at the Density Functional Theory (DFT) MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual DFT reactivity indices allows the explanation of the reactivity, and the chemo- and regioselectivity experimentally observed. The particular mechanism of this 32CA reaction involving low electrophilic ketenes has been elucidated by using a bonding evolution theory (BET) study. It is determined that this reaction takes place in one kinetic step only but in a non-concerted manner since two stages are clearly identified. Indeed, the formation of the se…
Understanding the domino reaction between 1-diazopropan-2-one and 1,1-dinitroethylene. A molecular electron density theory study of the [3 + 2] cyclo…
2017
The reaction between 1-diazopropan-2-one and 1,1-dinitroethylene has been studied using the Molecular Electron Density Theory (MEDT) at the B3LYP/6-31G(d,p) computational level. This reaction comprises two domino processes initialised by a common [3 + 2] cycloaddition (32CA) reaction yielding a 1-pyrazoline, which participates in two competitive reaction channels. Along channel I, 1-pyrazoline firstly tautomerises to a 2-pyrazoline, which by a proton abstraction and spontaneous loss of nitrite anion yields the final pyrazole, while along channel II, the thermal extrusion of the nitrogen molecule in 1-pyrazoline gives a very reactive diradical intermediate which quickly yields the final gem-…
How does the global electron density transfer diminish activation energies in polar cycloaddition reactions? A Molecular Electron Density Theory study
2017
Abstract The key role of the Global Electron Density Transfer (GEDT) in polar cycloaddition reactions is analysed within the Molecular Electron Density Theory (MEDT) using Density Functional Theory (DFT) calculations at the MPWB1K/6-311G(d) computational level. A comparative MEDT study of the non-polar Diels-Alder reaction between cyclopentadiene (Cp) and ethylene and the polar Diels-Alder reaction between Cp and tetracyanoethylene makes it possible to establish that the GEDT taking place in the direction of the transition state structures favours the bonding changes required for the formation of the new C C single bonds along polar cycloaddition reactions. Analysis of the reactivity indice…