Line drawing

Institute of Technology (MIT) [193]. Molecules were represented as line drawings on a homemade display (an oscilloscope (Figure 2-122). In addition, the system had diverse peripherals with many switches and buttons which allowed the modification of the scene. The heart of the. system was the. so-called Crystal Ball" which could rotate the molecule about all three orthogonal axes. This prototype cost approximately two million US dollars. 

Different systems may require different protocols to obtain one of many possible graphs, and several protocols in one system often achieve the same result. At entry level, all this may seem a bit bewildering, but to anyone who has struggled with mechanical drawing tools to make a simple line drawing like Fig. 1-8, SigmaPlot seems a miracle. 

ChemSketch has some special-purpose building functions. The peptide builder creates a line structure from the protein sequence defined with the typical three-letter abbreviations. The carbohydrate builder creates a structure from a text string description of the molecule. The nucleic acid builder creates a structure from the typical one-letter abbreviations. There is a function to clean up the shape of the structure (i.e., make bond lengths equivalent). There is also a three-dimensional optimization routine, which uses a proprietary modification of the CHARMM force field. It is possible to set the molecule line drawing mode to obey the conventions of several different publishers. 

The 23 line drawings in [130] are very helpful for most routine bonding and grounding applications and for many years have been reproduced in NPCA 803 [6j. The following two sections cover general nonroutine applications. Chapters 5 and 6 of this book address specific grounding applications and special cases where electrical continuity may be unexpectedly lost. 

Figure 8-32. Line drawing showing instrumentation locations for a rod drop monitor.

C atoms are labelled a-e (see text), (b), (c) Line drawings of the two enantiomers of C76 viewed along the short C2 rotation axis and illustrating the chiral D2 symmetry of the molecule. 

Using computers to display molecular structure is an attractive alternative to traditional line drawings for several reasons. First, the model displayed on a computer screen looks and behaves more like a real molecule than a drawing does. The computer model can be viewed from different angles, and different display formats can be used to show atomic positions, atomic volumes, and other features of interest. Second, the computer can produce a good model even when the student does not know how to make an accurate drawing. Thus, the student, working with a computer, can explore new areas of chemistry ... 

Determine the proper line size for a 350 equivalent feet vacuum jet suction line drawing air at 350°F, at a rate of 255 Ibs/hr with an initial pressure at the source of 0.6 in. Hg. Abs. Assume 10-in. pipe reading Figure 2-43. Note watch scales carefully. 

To determine (approximately) the desirable ton-miles before the first cutoff on a new line, draw a vertical line from the derrick height to the wireline size used. Project this line horizontally to the ton-mile figure given for the type of drilling encountered in the area. Subsequent cutoffs should be made at 100 ton-miles less than those indicated for iVs-in. and smaller lines, and at 200 ton-miles less than I A-in. and 1%-in. lines. 

Both of these structures satisfy the formal valence rules for carbon, but each has a serious fault. Each structure shows three of the carbon-carbon bonds as double bonds, and three are shown as single bonds. There is a wealth of experimental evidence to indicate that this is not true. Any one of the six carbon-carbon bonds in benzene is. the same as any other. Apparently the fourth bond of each carbon atom is shared equally with each adjacent carbon. This makes it difficult to represent the bonding in benzene by our usual line drawings. Benzene seems to be best represented as the superposition or average of the two structures. For simplicity, chemists use either one of the structures shown in (30) usually expressed in a shorthand form (SI) omitting the hydrogen atoms ... 

Make a graph with an energy scale extending on the ordinate from zero to 3000 kcal/mole and with the abscissa marked at equal intervals with the labels Na, Mg, and Al. Now plot and connect with a solid line the first ionization energies, Ei, of these three elements (see Table 20-IV). Hot Et and connect with a dashed line, E with a dotted line, and Et with a solid line. Draw a... 

Another way to visualize the data organization is to represent the row vector containing the absorbance spectrum as a line drawing —... 

The adiabatics are small curve-elements, which, for an infinitesimal cycle, may be regarded as parallel straight lines. Draw BF, CE perpendicular to the volume axis Or. 

Figure 55 Line drawing of structurally characterized Djf, and 2 isomers 16 and 17 of T)4H)4, and D4J isomer 18 of Each vertex represents an Si-H unit and each edge contains the...

Bond-line drawings show the carbon skeleton (the connections of all the carbon atoms that build up the backbone, or skeleton, of the molecule) with any functional groups that are attached, such as - OH or -Br. Lines are drawn in a zigzag format, where each comer or endpoint represents a carbon atom. For example, the following compound has 7 carbon atoms ... 

Now that we know how to count carbon atoms, we must learn how to count the hydrogen atoms in a bond-line drawing of a molecule. Most hydrogen atoms are not shown, so bond-line drawings can be drawn very quickly. Hydrogen atoms connected to atoms other carbon (such as nitrogen or oxygen) must be drawn ... 

Now we can understand why we save so much time by using bond-line drawings. Of course, we save time by not drawing every C and H. But, there is an even larger benefit to using these drawings. Not only are they easier to draw, but they are easier to read as well. Take the following reaction for example ... 

It is somewhat difficult to see what is happening in the reaction. You need to stare at it for a while to see the change that took place. However, when we redraw the reaction using bond-line drawings, the reaction becomes very easy to read immediately ... 

To draw this as a bond-line drawing, we focus on the carbon skeleton, making sure to draw any atoms other than C and H. All atoms other than carbon and hydrogen must be drawn. So the example above would look like this ... 

PROBLEMS For each structure below, draw the bond-line drawing in the box provided. 

When drawing a molecule, you should either show aU of the H s and all of the C s, or draw a bond-line drawing where the C s and H s are not drawn. You cannot draw the C s without also drawing the H s ... 

First, open your textbook and flip through the pages in the second half. Choose any bond-line drawing and make sure that you can say with confidence how many carbon atoms you see and how many hydrogen atoms are attached to each of those carbon atoms. 

Now that we have established that formal charges must always be drawn and that lone pairs are usually not drawn, we need to get practice in how to see the lone pairs when they are not drawn. This is not much different from training yourself to see all the hydrogen atoms in a bond-line drawing even though they are not drawn. If you know how to count, then you should be able to figure out how many lone pairs are on an atom where the lone pairs are not drawn. 

The examples above are clear, bnt with bond-line drawings, it can be more difficult to see the violation because we cannot see the hydrogen atoms (and, very often, we cannot see the lone pairs either for now, we will continne to draw lone pairs to ease you into it). You have to train yonrself to see the hydrogen atoms and to recognize when yon are exceeding an octet ... 

Answer It is important to recognize where all of the protons (hydrogen atoms) are. If you cannot do this, then you should review Chapter 1, which covers bond-line drawings. Only one proton can leave behind a negative charge in an sp orbital. All of the other protons would leave behind a negative charge on either sp or sp hybridized orbitals. So the most acidic proton is... 

Many compounds have double or triple bonds, and are said to be unsaturated because a compound with a double or triple bond has less hydrogen than it would have without the double or triple bond. These double and triple bonds are very easy to see in bond-line drawings ... 

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