Hourglassing

Sand-ton, m. sandy clay, -traube,/. bearberry. -uhr, /. sandglass, hourglass, -wiiste, /. sandy desert, -zucker, m. raw ground sugar, brown sugar. 

Imagine that you have an hourglass with two openings that the sand had to pass by ... 

The same is true in a two-step reaction. If the first step is slow and the second step is fast, then the speed of the second step is irrelevant. The rate of product formation will depend only on the rate of the first step (the slow step). So in our 8 1 reaction, the first step is the slow step (loss of the LG to form the carbocation) and the second step is fast (nucleophile attacking the carbocation). Just as we saw in the hourglass, the second step of our mechanism will not affect the rate of the reaction. Notice that the nucleophile does not appear in the mechanism until the second step. If we added more nucleophile, it would not affect the rate of the first step. Adding more nucleophile would only speed up the second step. But we already saw that the rate of the second step does not matter for the overall reaction rate. Speeding up the second step will not change anything. So the concentration of nucleophile does not affect the rate of the reaction. 

To picture the spatial distribution of an electron around a nucleus, we must try to visualize a three-dimensional wave. Scientists have coined a name for these three-dimensional waves that characterize electrons they are called orbitals. The word comes from orbit, which describes the path that a planet follows when it moves about the sun. An orbit, however, consists of a specific path, typically a circle or an ellipse. In contrast, an orbital is a three-dimensional volume for example, a sphere or an hourglass. The shape of a particular orbital shows how an atomic or a molecular electron fills three-dimensional space. Just as energy is quantized, orbitals have specific shapes and orientations. We describe the details of orbitals in Section 7-1. 

Hayashi, A., Olmstead, M.M., Attar, S. and Balch, A.L. (2002) Crystal chemistry of the Gold (I) trimer, Au3(NC5H4)3 formation of hourglass figures and self-assodation through aurophilic attraction. Journal of the American Chemical Society, 124, 5791-5795. 

I am repeating myself. Does time roll over as in an hourglass, the same sand as before When will God decide to break the glass, and shake the souls out, the better to pass judgment on them ... 

Figure 1 Time-dependent composition data is shown for the hydrogenation of aqueous 3-buten-2-ol for both (a) ultrasound irradiated and (b) magnetically stirred systems. The symbols correspond to experimental measurements (3-buten-2-ol 3BEN20L-solid circles 3-buten-2-one 3BEN20NE-open hourglass 2-butanone 2BONE-open triangles 2-butanol 2BOL-crossed squares). The lines in the ultrasound experiment simply connect the data points, whereas for the stirred experiment the lines correspond to a modeled fit (see text).

If l = 1, then the orbital is called a p-orbital with two lobes of high electron density on either side of the nucleus, for an hourglass or dumbbell shape. 

The next painting confronts her with humanity s greatest test—mortality itself. In front of a cave below the temple stands a giant muscular figure of Father Time he is winged and bearded with an hourglass perched on his head and the scythe of death held in his right hand. His intentions are obvious. 

Figure2.1 The hourglass structure of the IMRD format (adapted from Hill et al., 1982).

The hourglass icon is used in modules 1 and 2 as a visual reminder of the level of detail required at different points in your written work. 

Browse through three articles in Chemical Research in Toxicology or the Journal of Agricultural and Food Chemistry. For each article, copy and paste into a text document one sentence from each IMRD section that is consistent with the hourglass structure. Examine each group of four sentences. Is the hourglass structure apparent in these four sentences Explain. 

Most Methods sections follow a conventional organizational pattern. The pattern typically Involves two or three separate steps, each of which corresponds to a move, as shown in hgure 3.1. In accord with a common title for this section— Materials and Methods—the moves describe first the materials and then the methods (experimental and/or numerical) that were used in the work. Because these moves describe specific information, the Methods section is in the narrowest part of the IMRD hourglass structure. 

Is the last paragraph (P5) accessible to a scientific audience (as opposed to an expert audience), thereby completing the hourglass structure What larger implications do the authors present ... 

The Introduction begins with the most general information (the research area) and gradually shifts to a more specihc focus (the current work), preparing the reader for the highly specihc focus of the Methods section. This transition from general to specihc is apparent in the now-familiar hourglass shape of the journal article. 

The poster text is divided into the same general IMRD sections as the journal article Introduction, Methods, Results, and Discussion. Similarly, most posters include an Acknowledgments section, some have an abbreviated References section, and all have a title and author list. Most posters do not include an abstract, in part because of space limitations and in part because an abstract already appears in the conference proceedings. Like the journal article, the IMRD structure of the poster follows an hourglass shape. The top (Introduction) and bottom (Discussion) sections have a broader focus, while the middle sections (Methods and Results) have a narrower focus. Each section of the poster can be divided into individual moves or steps that guide viewers in a conventional way through the content of each section. These moves are analyzed in the next part of the chapter. 

The second move of the poster Introduction previews the specific accomplishments of the work and is often given its own subheading (e.g.. Research Objectives or Goals). The focus should be on research goals that have been achieved and are presented in the poster. Move 2 has a narrower focus than move 1 hence, the poster Introduction follows the broad-to-narrow hourglass structure. As a test to see if your Introduction addresses moves 1 and 2 sufficiently, ask yourself if a viewer, after reading only your Introduction, could answer the following questions (1) What research area is addressed (2) Why is this area important (3) What specific accomplishments will the authors present in their poster ... 

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