Pictorial representations

In Europe, the German standards organisation has published a set of guide rules and symbols for flow-sheet presentation, DIN 28004 (1988). This is available in an English translation from the British Standards Institution. 

---

Non-covalent interactions between molecules often occur at separations where the van der Waals radii of the atoms are just touching and so it is often most useful to examine the electrostatic potential in this region. For this reason, the electrostatic potential is often calculated at the molecular surface (defined in Section 1.5) or the equivalent isodensity surface as shown in Figure 2.18 (colour plate section). Such pictorial representations... 

Extensive discussions have focused on the conformation of the alkyl chains in the interior ". It has been has demonstrated that the alkyl chains of micellised surfactant are not fully extended. Starting from the headgroup, the first two or three carbon-carbon bonds are usually trans, whereas gauche conformations are likely to be encountered near the centre of tlie chain ". As a result, the methyl termini of the surfactant molecules can be located near the surface of the micelle, and have even been suggested to be able to protrude into the aqueous phase "". They are definitely not all gathered in the centre of tire micelle as is often suggested in pictorial representations. NMR studies have indicated that the hydrocarbon chains in a micelle are highly mobile, comparable to the mobility of a liquid alkane ... 

Models are the handiwork of theoreticians and may be mechanical or electrical analogs, pictorial representations, or purely mathematical constructs. 

All pictorial representations of molecules are simplified versions of our current model of real molecules, which are quantum mechanical, probabilistic collections of atoms as both particles and waves. These are difficult to illustrate. Therefore we use different types of simplified representations, including space-filling models ball-and-stick models, where atoms are spheres and bonds are sticks and models that illustrate surface properties. The most detailed representation is the ball-and-stick model. However, a model of a protein structure where all atoms are displayed is confusing because of the sheer amount of information present (Figure 2.9a). 

The lesson in these figures is that the qualitative concepts of chemical structures can be given a pictorial representation based on the quantitative application of the principles of quantum chemistry. Various, indeed all, molecular properties can, in principle, be calculated from the electronic distribution these pictures represent. 

A pictorial representation of the different fume capture techniques is shown in Fig. 13.33. 

Verm diagrams (Fig. 19.3.1) provide a pictorial representation of these events. 

For a preliminary survey of the electron density, it is usual to make a pictorial representation as we did in previous chapters. Whilst such diagrams do not carry much information, they do provide a theoretical measure which can be compared to the results of X-ray diffraction studies. A whole volume of the Transactions of the American Chemical Society (1972) was devoted to the Symposium Experimental and Theoretical Studies of Electron Densities . 

Assuming that the circles represent cations and squares represent anions, match the incomplete net ionic equations to their pictorial representations... 

The next most important aspect of a molecular compound is its shape. The pictorial representations of molecules that most accurately show their shapes are images based on computation or software that represents atoms by spheres of various sizes. An example is the space-filling model of an ethanol molecule shown in Fig. C.2a. The atoms are represented by colored spheres (they are not the actual colors of the atoms) that fit into one another. Another representation of the same molecule, called a ball-and-stick model, is shown in Fig. C.2b. Each ball represents the location of an atom, and the sticks represent the bonds. Although this kind of model does not represent the actual molecular shape as well as a space-filling model does, it shows bond lengths and angles more clearly. It is also easier to draw and interpret. 

A pictorial representation of the Tg-S mixing process follows from Fig. 6. Just as in normal n.m.r. or e.s.r. spectroscopy, precession can be represented by a vector model. When placed in an external magnetic field the two unpaired electrons of the radical pair 1 and 2 will precess... 

Note Although these three pictorial representations look exactly the same, the particles actually acted differently in still motion than when vibrating. 

Figure 3.1 gives a hand-drawn pictorial representation of the general classes of polymer-inorganic hybrids. 

See, J.L. Leblanc, Insight into elastomer—filler interactions and their role in the processing behaviour of mbber compounds, Prog. Rubber Plast. TechnoL, 10/2, 110-129, 1994, for a pictorial representation of such a morphology. 

Figure 2.60 Pictorial representation of the SLIC scheme showing the updating scheme for an upwind and a downwind cell. Cells filled with fluid 1 are indicated in gray, those with fluid 2 in white. Cells containing a mixture of both fluids are represented by hatched areas. In the right column the configuration at the new time step is shown, with interface positions depicted explicitly.

Davis, Tenney L. Pictorial representations of alchemical theory. Isis 28, no. 1 (Feb 1938) 73-86. 

Figure 12,1 Pictorial representation of various types of mixing ...

A block diagram is a pictorial representation of the cause and effect relationship between the input and output of a physical system. A block diagram provides a means to easily identify the functional relationships among the various components of a control system. 

The overall results of substituent effects are observed in the products of a reaction, their rates of formation, and their stereochemistries. The purpose of this article is to apply very simple theoretical techniques to correlations and predictions of the rate and stereoselectivity effects of substituents in [2+2] photocycloadditions. The theoretical methods that will be used are perturbational molecular orbital (PMO) theory and its pictorial representation, the interaction diagram. Only an outline of the theory will be given below, since several more detailed descriptions are available. 4,18-34)... 

---