Bond-line drawings drawing

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 ... 

There is an entirely different way to draw stereocenters (instead of using regular bond-line drawings with dashes and wedges). Fischer projections are helpful for drawing molecules that have many stereocenters, one after another. These drawings look like this ... 

This compound can undergo two possible elimination reactions (to make it easier to see, we are drawing the H that gets eliminated in each case, even though we usually do not draw hydrogen atoms on bond-line drawings) ... 

Remember that in bond-line drawings, it is not necessary to draw the H that was added. 

The hydrogen atoms that were added are not explicitly shown, but remember that H s don t need to be drawn in bond-line drawings. You should be able to see them, even though they are not drawn. 

Be careful. The example above represents somewhat of an optical illusion. The products seem to suggest an anti addition (the methyl and the OH are trans to each other). But think about what we added in this reaction we did not add OH and a methyl group. The methyl group was already there. Rather, we added OH and H. The H that we added is not shown in the product above (because it does not have to be drawn in a bond-line drawing). If you draw that H on the compound above, you will see that it is on a dash—therefore, this was a syn addition of H and OH. 

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