Organic Chemistry As a Second Language PDF, 3E Free Download


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Organic Chemistry As a Second Language PDF 3rd Edition: First Semester Topics Free Download Download for free here: Additional tags: David Klein david klein organic chemistry Organic Chemistry As a Second Language first semester topics Organic Chemistry As a Second Language pdf organic chemistry klein organic chemistry klein ebook Organic Chemistry As a Second Language pdf download

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To do well in organic chemistry you must first learn to interpret the drawings that organic chemists use. When you see a drawing of a molecule it is absolutely criti- cal that you can read all of the information contained in that drawing. Without this skill it will be impossible to master even the most basic reactions and concepts. Molecules can be drawn in many ways. For example below are three different ways of drawing the same molecule: Without a doubt the last structure bond-line drawing is the quickest to draw the quickest to read and the best way to communicate. Open to any page in the second half of your textbook and you will find that every page is plastered with bond-line drawings. Most students will gain a familiarity with these drawings over time not realizing how absolutely critical it is to be able to read these drawings fluently. This chapter will help you develop your skills in reading these drawings quickly and fluently. 1.1 HOW TO READ BOND-LINE DRAWINGS 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 corner or endpoint represents a carbon atom. For example the following compound has 7 carbon atoms: It is a common mistake to forget that the ends of lines represent carbon atoms as well. For example the following molecule has six carbon atoms make sure you can count them: CH 3 2 CHCHCHCOCH 3 C C C C C O C C O H H H H H H H H H H H H 1 CHAPTER1 BOND-LINE DRAWINGS

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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: It is common to see a small gap on either side of a triple bond like this: Both drawings above are commonly used and you should train your eyes to see triple bonds either way. 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: 1 O 2 3 4 5 6 1 2 3 4 5 O CC C C H H H H H H is drawn like this: CC C C H H H H H H H H H H is drawn like this: is the same as C C is the same as so this compound has 6 carbon atoms 2 CHAPTER 1 BOND-LINE DRAWINGS

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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 con- nected to atoms other carbon such as nitrogen or oxygen must be drawn: But hydrogen atoms connected to carbon are not drawn. Here is the rule for deter- mining how many hydrogen atoms there are on each carbon atom: neutral carbon atoms 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 per- son 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 We only see two bonds connected to this carbon atom SH OH N H 1.1 HOW TO READ BOND-LINE DRAWINGS 3 O N N 1.2 Answer: 1.3 Answer: 1.4 Answer: 1.5 Answer: 1.6 Answer: 1.7 Answer: O O 1.8 Answer: 1.9 Answer: 1.1 1 Answer: 1.10 Answer: PROBLEMS Count the number of carbon atoms in each of the following drawings. OH O

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bonds to the carbon atom. After doing this many times you will get to a point where you do not need to count anymore. Y ou 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. EXERCISE 1.12 The following molecule has nine carbon atoms. Count the num- ber 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. 1bond 3Hs 1 bond 3Hs 1 bond 3Hs 4 bonds no Hs 4 bonds no Hs 4 bonds no Hs 2 bonds 2Hs 3 bonds 1H O 4bonds no Hs O 4 CHAPTER 1 BOND-LINE DRAWINGS O 1 1 2 2 2 0 1.13 1.17 1.18 1.19 1.20 1.14 1.15 1.16 O O

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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 ben- efit 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: O C C C C O C CH 3 CH 3 H H H H H H H H H 2 Pt O O CH 3 2 CCHCOCH 3 H 2 Pt CH 3 2 CHCH 2 COCH 3 1.2 HOW TO DRAW BOND-LINE DRAWINGS 5

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Synthesis is really just the flipside of predicting products. In any reaction there are three groups of chemicals involved: the starting material the reagents and the products: When the products are not shown then you have a “predict the product” problem: When the reagents are not shown then you have a synthesis problem: Synthesis problems can be easy if they are only one step or they can be dif- ficult if they are more than one step. When you begin learning reactions in your course you will start to encounter synthesis problems in your textbook. At first you will get one-step problems and as the course progresses you will see multistep syntheses. In a multistep synthesis you can often end up with a product that looks very different from the starting material. For example look at the following series of reactions below. Don’t concentrate on how the changes were made. For now just focus on the fact that each reaction changes the compound only slightly but in the end we end up with a product completely different from the starting material: Br O O O Starting Material Product Starting material Products Starting material Reagents Starting material Reagents Products 332 CHAPTER13 SYNTHESIS

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13.1 ONE-STEP SYNTHESES 333 It can only take three or four steps before the problem can get quite difficult. If you convert the sequence above into a synthesis problem it would look like this: If you are having trouble with synthesis problems when you first encounter them the worst thing you can do is to give up and say: “Oh well I’m not good at synthesis problems.” As the course moves on this attitude will slowly kill your grade in the course. To see why this is so let’s compare organic chemistry to a game of chess. Imagine that you are learning how to play chess. You first learn about the pieces: how they are named how to set up the board and so on. Then you learn how each piece moves and how they capture each other. When you start playing your first game you realize that there is quite a bit of strategy involved. Most strategies in- volve thinking more than just one move in advance. It is not good enough to know only how to move the pieces. You also need to think about how to plan out the next few moves so that you can coordinate an attack on your opponent’s pieces. Imagine how silly it would be to take the time to learn how to move the pieces but to then say to yourself that you are not good at strategy. Imagine thinking that you will keep playing chess but you just won’t be good at that one aspect of the game. That would be silly because that one aspect of the game is the whole game itself. Y ou either need to learn how to strategize or just don’t play chess. There is no in-between. Organic chemistry is very much the same. Synthesis is all about strategizing. You need to think a few moves ahead and you must learn how to do this. You can- not tell yourself that you are not good at synthesis problems and therefore you will just focus on the other aspects of organic chemistry. Synthesis is organic chemistry. The second half of the course is all about learning reactions and applying them in syntheses. Everything that you have learned so far has prepared you for synthesis. The only way to become proficient at synthesis is to practice. Don’t be lazy and don’t think that you can get through the course without learning how to propose syntheses. If you do you will find that your performance in the course will spiral down to a point that will make you very unhappy. There are a few techniques that will make you feel more comfortable with syn- thesis problems and there are exercises that you can go through to increase your pro- ficiency in doing synthesis problems. That’s what this chapter is all about. 13.1 ONE-STEP SYNTHESES As we mentioned earlier one-step syntheses are the first synthesis problems you will encounter. They will never be more difficult than predicting products. Before you can move on to multistep syntheses you first need to feel comfortable with one-step syntheses. O

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To do this we need to make a list of reactions but we will leave out the reagents so that we can repeatedly photocopy the list and get practice filling in the reagents. As you learn more and more reactions this list will grow. With every five new reactions you should photocopy all of the reactions that you have recorded here. Then start filling in the reagents on the photocopy. Repeat this procedure whenever you have entered five new reactions. If you keep up with this exercise as the course progresses you will be in very good shape for solving one-step synthesis problems. The hardest challenge that you will face is keeping up with the work and not waiting until the night before the exam. If you wait as most students do you will find it very difficult to spend the time that it takes to master this material. Don’t make that mistake. The secret to success in this course is to do a little bit every night rather than cramming on the night before the exam. Cramming might work well for other courses but it doesn’t work well in or- ganic chemistry. Begin your list on the next page. For now skip forward a few pages. We have some techniques to go over that will help you solve synthesis problems. 334 CHAPTER 13 SYNTHESIS

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13.1 ONE-STEP SYNTHESES 335 Remember not to fill in the reagents or the mechanisms. For each reaction just draw the starting material in front of the arrow and the products after the arrow. Leave the space above the arrow empty. You will fill in the reagents when you photocopy these pages:

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Now photocopy this page and try to fill in the reagents on your photocopied page. Now photocopy this page again and fill in the reagents for every reaction on this page. 336 CHAPTER 13 SYNTHESIS

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