2 CHAPTER 1 BOND-LINE DRAWINGS Double bonds are shown with two lines,and triple bonds are shown with three lines: When drawing triple bonds,be sure to draw them in a straight line rather than zigzag. because triple bonds are linear(there will be more about this in the chapter on geom- etry).This can be quite confusing at first,because it can get hard to see just how many carbon atoms are in a triple bond,so let's make it clear: so this compound has is the same as 6 carbon atoms Don't let triple bonds confuse you.The two carbon atoms of the tripe bond and the two carbon connected to them are drawn in a straight line.All other bonds are drawn as a zigzag: HHHH H-C-C-C-C-H is drawn like this: HHHH BUT H H-C-C=C-C-H is drawn like this: H EXERCISE 1.1 Count the number of carbon atoms in each of the following drawings: Answer The first compound has six carbon atoms,and the second compound has five carbon atoms: PROBLEMS Count the number of carbon atoms in each of the following drawings
Double bonds are shown with two lines, and triple bonds are shown with three lines: When drawing triple bonds, be sure to draw them in a straight line rather than zigzag, because triple bonds are linear (there will be more about this in the chapter on geometry). This can be quite confusing at first, because it can get hard to see just how many carbon atoms are in a triple bond, so let’s make it clear: Don’t let triple bonds confuse you. The two carbon atoms of the triple bond and the two carbons connected to them are drawn in a straight line. All other bonds are drawn as a zigzag: BUT EXERCISE 1.1 Count the number of carbon atoms in each of the following drawings: Answer The first compound has six carbon atoms, and the second compound has five carbon atoms: PROBLEMS Count the number of carbon atoms in each of the following drawings. 1 O 2 3 4 5 6 1 2 3 4 5 O C C C C H H H H H H is drawn like this: C C C C H H H H H H H H H H is drawn like this: C C is the same as so this compound has 6 carbon atoms 2 CHAPTER 1 BOND-LINE DRAWINGS 6753_Klein_01.qxd 5/1/07 5:03 PM Page 2
1.1 HOW TO READ BOND-LINE DRAWINGS 3 女3&8 Answer:_ 3 Answer: 1.4 Answer:_ Answer 1.6 Answer:_ 1.7 Answer:_ 1.8 Answer:_ 1.9 Answer: 入0入 1.10 Answer:_1.11 Answer:_ 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.The hydrogen atoms are not shown,and this is why it is so easy and fast to draw bond-line drawings.Here is neutral carbon atoms always ha We see only two bonds connected to this carbon atom Therefore,it is assumed that there are two more bonds to hydrogen atoms(to give a total of four bonds).This is what allows us to avoid drawing the hydrogen atoms and to save so much time when drawing molecules.It is assumed that the average per- son knows therefore is capable of the umber of hydrogen atoms even though they are not shown. So you only need to count the number of bonds that you can see on a carbon atom,and then you know that there should be enough hydrogen atoms to give a total of four bonds to the carbon atom.After doing this many times,you will get to a point where you do not need to count anymore.You will simply get accustomed to seeing these types of drawings.and you will be able to instantly"ee all of the hydrogen atoms without counting them.Now we will do some exercises that will help you get to that point
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. The hydrogen atoms are not shown, and this is why it is so easy and fast to draw bond-line drawings. Here is the rule for determining how many hydrogen atoms there are on each carbon atom: neutral carbon atoms always have a total of four bonds. In the following drawing, the highlighted carbon atom is showing only two bonds: Therefore, it is assumed that there are two more bonds to hydrogen atoms (to give a total of four bonds). This is what allows us to avoid drawing the hydrogen atoms and to save so much time when drawing molecules. It is assumed that the average person knows how to count to four, and therefore is capable of determining the number of hydrogen atoms even though they are not shown. So you only need to count the number of bonds that you can see on a carbon atom, and then you know that there should be enough hydrogen atoms to give a total of four bonds to the carbon atom. After doing this many times, you will get to a point where you do not need to count anymore. You will simply get accustomed to seeing these types of drawings, and you will be able to instantly “see” all of the hydrogen atoms without counting them. Now we will do some exercises that will help you get to that point. O We see only two bonds connected to this carbon atom 1.1 HOW TO READ BOND-LINE DRAWINGS 3 O O OH N H O O OH 1.2 Answer: 1.3 Answer: 1.4 Answer: 1.5 Answer: 1.6 Answer: 1.7 Answer: O 1.8 Answer: 1.9 Answer: 1.11 Answer: O 1.10 Answer: 6753_Klein_01.qxd 5/1/07 5:03 PM Page 3
4 CHAPTER 1 BOND-LINE DRAWINGS EXERCISE 1.12 The following molecule has 14 carbon atoms.Count the num- ber of hydrogen atoms connected to each carbon atom. Answer: 4 bonds.4 bonds. ∴.noH's ∴noHs 4 bonds 1 bond, ∴.noHs ∴.3Hs 4 bonds, .'.no H's 1 bond, .3H's 3 bonds. ..1H 3 bonds 1 bond ..1H 4 bonds, .'.noH's PROBLEMS For each of the following molecules,count the number of hydroger atoms connected to each carbon atom.The first problem has been solved for you (the numbers indicate how many hydrogen atoms are attached to each carbon). 出
EXERCISE 1.12 The following molecule has 14 carbon atoms. Count the number of hydrogen atoms connected to each carbon atom. Answer: PROBLEMS For each of the following molecules, count the number of hydrogen atoms connected to each carbon atom. The first problem has been solved for you (the numbers indicate how many hydrogen atoms are attached to each carbon). O 1 bond, 3 H’s 1 bond, 3 H’s 1 bond, 3 H’s 1 bond, 3 H’s 4 bonds, no H’s 4 bonds, no H’s 4 bonds, no H’s 4 bonds, no H’s 4 bonds, no H’s 2 bonds, 2 H’s 3 bonds, 1 H 3 bonds, 1 H 3 bonds, 1 H 3 bonds, 1 H O 4 CHAPTER 1 BOND-LINE DRAWINGS O 1 1 2 2 2 0 N H O O OH O 1.13 1.17 1.18 1.19 1.20 1.14 1.15 1.16 6753_Klein_01.qxd 5/1/07 5:03 PM Page 4
1.2 HOW TO DRAW BOND-LINE DRAWINGS 5 Now we can understand why we save so much time by using bond-line drawings.Of rse,we save time by not drawing very C and H.Bu there is an even larger efit to usi rawings.Not only are they easier to draw,but they are easier to read as well.Take the following reaction for example: H2 (CH3)2CH=CHCOCH3 (CH3)2CH2CH2COCH3 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 reac- tion using bond-line drawings,the reaction becomes very easy to read immediately H2 0 Pt As soon as you see the reaction,you immediately know what is happening.In this reaction we are converting a double bond into a single bond by adding two hydro- gen atoms across the double bond.Once you get comfortable reading these draw- ings.you will be better equipped to see the changes taking place in reactions. 1.2 HOW TO DRAW BOND-LINE DRAWINGS C-CH3 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: HH H-C H-0 C-CHa H HH CH3
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: As soon as you see the reaction, you immediately know what is happening. In this reaction we are converting a double bond into a single bond by adding two hydrogen atoms across the double bond. Once you get comfortable reading these drawings, you will be better equipped to see the changes taking place in reactions. 1.2 HOW TO DRAW BOND-LINE DRAWINGS Now that we know how to read these drawings, we need to learn how to draw them. Take the following molecule as an example: 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: C C C C O C CH3 CH3 HH H H H H H H O C C C C O C CH3 CH3 HH H H H H H H O H2 Pt O (CH3)2CH=CHCOCH3 H2 Pt (CH3)2CH2CH2COCH3 1.2 HOW TO DRAW BOND-LINE DRAWINGS 5 6753_Klein_01.qxd 5/1/07 5:03 PM Page 5
6 CHAPTER 1 BOND-LINE DRAWINGS A few pointers may be helpful before you do some problems. 1.Don't forget that carbon atoms in a straight chain are drawn in azigzag format H-C-C-C-C-H is drawn like this: HHHH 2.When drawing double bonds,try to draw the other bonds as far away from the double bond as possible: is much better than BAD 3.When drawing zigzags,it does not matter in which direction you start drawing: is the same as 人is the same as PROBLEMS For each structure below,draw the bond-line drawing in the box provided H H-C-C-C-0 HHH H 1.21 HHH C OH H-C-C-C H HUH 1.22 (CH3)3C-C(CH3)3 1.23
A few pointers may be helpful before you do some problems. 1. Don’t forget that carbon atoms in a straight chain are drawn in a zigzag format: 2. When drawing double bonds, try to draw the other bonds as far away from the double bond as possible: BAD 3. When drawing zigzags, it does not matter in which direction you start drawing: PROBLEMS For each structure below, draw the bond-line drawing in the box provided. is the same as is the same as O O is much better than C C C C H H H H H H H H H H is drawn like this: 6 CHAPTER 1 BOND-LINE DRAWINGS C C C H H H H H H H C H H C C H H H C H H H C H H H H C C H H H C H H H C O C H H H (CH3)3C–C(CH3)3 1.22 1.23 1.21 6753_Klein_01.qxd 5/1/07 5:03 PM Page 6