How to Study Organic Chemistry ------------------------------------------------------------------------ Most students consider organic chemistry to be one of the most difficult courses that they take during their college career. Some consider it to be challenging but fun (much like a game of chess can be) but others find it to be impossibly difficult. The material can be mastered and is, in fact, not conceptually difficult. The first difficulty that students encounter is the amount of information that they are expected to learn. Organic chemistry is a very vigorous field and much has already been discovered about organic compounds and their reactions. Many organic text books are now about 1400 pages long. You cannot expect to learn all this material without investing considerable time and effort in studying. The pace of the course is brisk and allowing yourself to fall behind in your studying will spell doom for most students. Unlike general chemistry, the introductory organic courses (355 and 356) contain little math. What then, does this vast volume of information consist of? What are organic chemists interested in knowing and what do they know? First, organic chemists are interested in the structure of organic molecules. Your previous study of bonding (particularly covalent bonding) will be reviewed and used extensively in this course. Organic chemists are also very interested in the three dimensional shapes of molecules. The branch of organic chemistry that deals with three dimensional shape is called stereochemistry and will be a very important part of the course. Second, organic chemists are very interested in chemical reactions. By the end of the second course (356), you will have learned hundreds or even thousands of reactions. In learning these reactions, you will want to know what products will be obtained if two compounds are mixed under a given set of conditions and also what kinds of reagents can be used to cause certain types of reactions to occur. Third, for many reactions we will study, the details of how the reactions occur are known. When a reaction occurs one must first know what reagents were used as starting materials and what the final products are. The conversion of the starting materials to the products will involve either breaking bonds, making bonds or both. The detailed sequence of which bonds are broken and formed, in what order, and the stereochemical relationships of these bonds is called a mechanism for the reaction. Understanding mechanisms is the key to modern organic chemistry. Although we will be studying hundreds or even thousands of reactions, these reactions occur via only a few fundamental mechanistic pathways. It is the recognition of the mechanistic similarities between different reactions that allows organic chemistry to be readily understood. Many students who find organic chemistry impossibly difficult never appreciate this. It is as if you were given a copy of the New York City phone book that had been cut into pieces containing one name each and asked to put the names in the order in the book. Based on experience with some students in organic chemistry, a surprising number would get a complete phone book, attempt to memorize it, and then attempt to put the names in the order of the list they had memorized. This is the reason that a surprising number of students find organic chemistry impossibly difficult. Just as learning the alphabet and the rules for alphabetization will help in assembling the phone book, understanding mechanisms will help make sense of the thousands of facts that comprise organic chemistry. Your text book is organized primarily by types of compounds. Each type of compound will contain a specified substructure or functional group. For example, all the compounds of the type called alcohols contain an -OH group (the functional group for alcohols) bonded to a carbon atom. As we study each type of functional group, you will find that each reacts by only a few mechanistic paths and hence has a chemical "personality" of its own. Do not treat mechanisms as just another thing to memorize. Organic chemistry is a vast field and you must be able to see the forest for the trees. Mechanism and structure provide a way of doing this. Now let us suppose that you have learned the structures of organic compounds, what reactions various compounds undergo, what reagents cause certain types of reactions and have a good grasp of known mechanisms. Have you mastered organic chemistry? Are you now an organic chemist? Do you deserve an "A" in the course? Not yet! Working organic chemists do not just repeat what is known. They use that knowledge to solve problems and discover new chemistry. This course will be just as much about learning to solve problems and apply the knowledge you have gained as it will be about becoming familiar with what organic chemists have learned. An analogy would be a course in the game of chess. In such a course you would be expected to play chess. A simple knowledge of the rules, recognition of the pieces and a knowledge of what moves each piece is allowed would not be enough. Similarly, in this course, you will be required to use the knowledge you have gained in new and creative ways (both in the homework and in the exams). Organic chemistry is as much or more about learning to think in a chemical context as it is about the context itself. The types of problems that organic chemists encounter are many and varied. However, there are three types of problems that commonly occur and that you will often have to solve. The first of these is identifying an unknown substance. This can be done by studying the reactions that the compound does or does not do. To solve this type of problem, you must learn chemical reactions in the forward sense. That is, you must know what will happen if two compounds are mixed. A second approach to this type of problem is to identify the compound through spectroscopy. Spectroscopy involves subjecting the molecule to some energy source (there are several types commonly used) and determining how it interacts with the energy source. A second major type of problem encountered by organic chemists is that of preparing (making) a given compound. To work synthesis problems, it is useful to learn chemical reactions in a reverse sense. That is, if you need to make a given type of compound, you must know what types of reactions and what starting materials to use to get it. Often the compound to be synthesized is complicated enough that it cannot be made in a single reaction -- rather a series of reactions is needed. In such a multi-step synthesis, it is often useful to work backwards. That is, one first thinks of all the ways of preparing the final product even if they do not use acceptable starting materials (allowed compounds in homework problems or compounds that are available in the laboratory). If none of the routes contains acceptable starting materials, you then devise syntheses of those starting materials. This process is then repeated until you find a route back to acceptable starting materials. The third major type of problem is explaining how a reaction occurs. The first step is to propose a reasonable mechanism. One then devises tests to check the proposed mechanism. In this course, more emphasis will be placed on proposing a reasonable mechanism than on devising tests to see if your mechanism is correct. As we study the mechanisms of known reactions, you will note that each functional group has characteristic ways in which it reacts. In most of the problems you will encounter, the individual steps of a proposed mechanism should be consistent with the known types of reactions for that functional group. Although it is possible, that the reaction involves a completely new and different kind of reactivity, it is much more likely that the individual steps are similar to known reactions. This will be true for two reasons: 1. Many homework and test questions will be at least somewhat related to what we have done, and 2. Organic chemists have already discovered many of the fundamental types of reactivity for the types of compounds we will be studying. To master organic chemistry, you will need to study regularly and systematically. The following technique is useful for many people: 1. Read ahead. When you come to class you should have read the material that will be presented. 2. Work the problems in the chapters (as opposed to those at the end of the chapters) as you read the material. Write out the answers on paper. Even if the answers seem obvious, writing them down will help you remember. 3. When working problems, work several problems before consulting the answer book. If you look up each answer as you do the problem you cannot help catching a glimpse of the answer to the next problem. The result is that you are not really working the next problem. 4. The first few problems at the ends of the chapters are there to help you to become familiar with the new material and to help you remember it. Look up the answers as needed. Again, write out the answers. 5. Prepare a set of flash cards to help you remember the reactions. Design these cards to help you remember reactions in both the forward and backward sense. Organic chemistry is a very cumulative subject. At the end of the second course (356) you will need to know to know the material presented on the first day of the first course (355) just as much as you will on the first exam. These cards will be invaluable for reviewing. NOTE WELL: Using flash cards prepared by another student will give you some benefits but much of the benefit of the flash cards comes from you having to think about the reaction enough to prepare the card. 6. Solve the more challenging problems at the ends of the chapters. The answers to most of these problems will not be obvious to you when you first read the question. Do not give up too quickly. Do not consult the answer book without making a determined effort to solve the problem on your own. Many people can read an answer and understand it. Do not be fooled into thinking you can solve problems because you understand the answers when you see them. Write the solutions out on paper. 7. Regular study will pay off much better than last minute cramming. You will get much better results by studying a hour each and every day as opposed to several hours once or twice a week. 8. Before exams review your flash cards and problems. Get a good nights sleep. You will be expected to solve new problems on the exams. If you have studied regularly, being alert and relaxed will be more important than last minute cramming. If you haven't studied regularly, you will be in trouble either way. ------------------------------------------------------------------------ [Department of Chemistry] ------------------------------------------------------------------------ chemistry@marshall.edu