Edge orientation

How do orbital symmetry requirements relate to [4tc - - 2tc] and other cycloaddition reactions Let us constmct a correlation diagram for the addition of butadiene and ethylene to give cyclohexene. For concerted addition to occur, the diene must adopt an s-cis conformation. Because the electrons that are involved are the n electrons in both the diene and dienophile, it is expected that the reaction must occur via a face-to-face rather than edge-to-edge orientation. When this orientation of the reacting complex and transition state is adopted, it can be seen that a plane of symmetry perpendicular to the planes of the... 

EC mechanism, 34, 42, 113 E. Coli, 186 Edge effect, 129 Edge orientation, 114 Electrical communication, 178 Electrical double layer, 18, 19 Electrical wiring, 178 Electrocapillary, 22 Electrocatalysis, 121 Electrochemical quartz crystal, microbalance, 52 Electrochemihuiiinescence, 44 Electrodes, 1, 107... 

A distinct answer has been found, however, with respect to the influence of crystallographic orientation of pyrolytic graphite on the rates of various reactions. It could be shown that the rate of cathodic oxygen reduction at the basal plane of graphite is much lower than at surfaces with edge orientation (Morcos and Yeager, 1970). To the contrary, the rates of simple redox reactions hardly depend on face orientation. 

Figure 2. [CuChJ2 absorption edge. Orientation of the CuClk unit showing the definition of the angle with respect to the polarization direction ->p (top), and spectra of CuCl2 in the orientations that minimize (=0°) and maximize (=45°)...

Figure 8 Cyclic voltammograms of cytochrome c recorded at an edge-oriented pyrolitic graphite electrode. In the absence (a) and in the presence (b) of [Cr(NH3)6]3 +...

Figure 24 Square wave voltammograms recorded at an edge-oriented pyrolytic graphite electrode in buffered aqueous solutions of [3Fe-4S] aconitase. (a) pH 6.2 (b) pH 7.5 (c) pH 8.2. Scan rate 0.1 V s ...

Figure 27 Cyclic voltammograms recorded at an edge-oriented pyrolitic graphite...

Figure 2.11 A simple cell responds to lines or edges oriented at a particular orientation. It may be constructed by receiving input from several of the center-surround neurons found in the lateral geniculate nucleus. (Reproduced from D. H. Hubei and T. N. Wiesel. Receptive fields, binocular interaction and functional architecture in the cat s visual cortex. Journal of Physiology, Vol. 160, pp. 106-154, 1962, by permission of Blackwell Publishing, UK.)...

Graph edges oriented in a definite direction which indicates the order of interconnection between the nodes are called directed arcs. Their orientation is indicated by the arrows placed either on the arcs or near them. A graph, a cycle, and a tree containing directed arcs are called directed. A directed cycle is also called a contour. 

Interaction goes along widely different ways in the catalyst systems studied CoPc molecules lie flat on the surface of alumina and alumina-rich supports and edge oriented on the surface in silica and silica-rich samples. 

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