Electron-transport properties of cyclophanes are investigated with qualitative Hückel molecular orbital analysis for better understanding of the intermolecular interaction in molecular devices. Charge and electron transfers often take place via through-space interactions, which are observed both in large biological molecules and in organic molecular crystals. Since the intermolecular electronic coupling in ³-stacked structures plays an important role in total device performance, in this work [2,2]paracyclophane is studied to investigate the effect of the intermolecular interactions in aromatic hydrocarbons on its electron-transport properties. According to the orbital symmetry rule, the symmetry-allowed and symmetry-forbidden connections for electron transport between the benzene rings are predicted just from the phase and amplitude of the frontier orbitals. The meta connection is symmetry allowed for electron transport while the para and ortho connections are symmetry forbidden. The qualitative predictions made with the Hückel approximation are found consistent with the calculation results obtained with density functional theory. The qualitative but essential understanding in the orbital views would extend the application of the rule from a single molecule to a crystal structure for the development of high-performance molecular devices.
The mechanisms of trifluoromethylation with hypervalent iodine trifluoromethylation reagent (Togni's reagent 1) have been comprehensively studied by density functional theory (DFT) calculations. The results show that there are two general reaction modes for reagent 1: (I) Mode-A, acting as a CF 3• free radical source. When one-electron reductants are available in the reaction system, such as Cu I , Fe II , TEMPONa, or electron-rich lithium enolate, 1 will be reduced via single-electron transfer (SET) and give out CF 3• free radical concertedly. In the Cu I -catalyzed trifluoromethylation of terminal olefins, Cu I promotes the homo-cleavage of the F 3 C−I bond in 1 via SET to produce Cu II species and CF 3• free radical. Then the CF 3• free radical attacks the olefin, leading to trifluoromethyl alkyl radical intermediate. Subsequently, the Cu II species act as a one-electron oxidant oxidizing the alkyl radical to carbocation intermediate, and the following deprotonation leads to the final product. Other mechanisms, such as formation of F 3 C−Cu III species via oxidative addition, formation of allylic radical intermediate, were considered and excluded. (II) Mode-B, acting as a CF 3 + cation source. 1 can be activated by a Lewis acid such as Zn II and becomes more inclined to undergo an S N 2 type nucleophilic attack at the CF 3 group by nucleophiles (pentanol in this work). For substrates studied in this paper, such as the lithium enolate, pentanol, and sodium 2,4,6-trimethylphenolate, the competition between their reducibility and nucleophilicity determines the reaction mode of regent 1.
In this work electron-transport properties of π-conjugated polycyclic aromatic hydrocarbons with different molecular sizes and edge type structures are investigated. The applicability of a derived concept for orbital control of electron transport (J. Am. Chem. Soc. 2008, 130, 9406) is tested on larger hydrocarbons in order to estimate its predictive power for different types of compounds. Favorable connections for effective electron transport in π-conjugated systems with weak coupling between the molecules and electrodes are predicted on the basis of the orbital symmetry rule by looking at the phase and amplitude of the frontier orbitals. Qualitative predictions based on frontier orbital analysis are compared with density functional theory calculations for realistic molecular junctions with strong covalent bonds between a molecule and two gold electrodes. Obtained results are in good agreement with the orbital symmetry rule predictions, which makes the frontier orbitals' analysis a powerful tool in electron transport studies in π-conjugated polycyclic aromatic hydrocarbons.
Intensive care units Intuition Heuristics Physical restraint a b s t r a c t Physical restraint is a common nursing intervention in intensive care units and nurses often use it to ensure patients' safety and to prevent unexpected accidents. However, existing literature indicated that the use of physical restraint is a complex one because of inadequate rationales, the negative physical and emotional effects on patients, but the lack of perceived alternatives. This paper is aimed to interpret the clinical decision-making theories related to the use of physical restraint in intensive care units in order to facilitate our understanding on the use of physical restraint and to evaluate the quality of decisions made by nurses. By reviewing the literature, intuition and heuristics are the main decision-making strategies related to the use of physical restraint in intensive care units because the rapid and reflexive nature of intuition and heuristics allow nurses to have a rapid response to urgent and emergent cases. However, it is problematic if nurses simply count their decision-making on experience rather than incorporate research evidence into clinical practice because of inadequate evidence to support the use of physical restraint.Besides that, such a rapid response may lead nurses to make decisions without adequate assessment and thinking and therefore biases and errors may be generated. Therefore, despite the importance of intuition and heuristics in decision-making in acute settings on the use of physical restraint, it is recommended that nurses should incorporate research evidence with their experience to make decisions and adequate assessment before implementing physical restraint is also necessary.
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