- What You Will Learn in Organic Chemistry
- Structure/Property Relationships
- Nomenclature
- Reactions
- Synthesis
- Mechanisms
- What You Should Have Learned in General Chemistry
- Atomic structure and Periodic Trends
- Bonding and Molecular Geometry
- Electronegativity and Molecular Polarity
- Acid-Base Concepts
- Equilibrium, Kinetics, and Thermodynamics
- How to Succeed in Organic Chemistry
- Top Ten Tips
- How to Succeed in Structure/Property Relationships
- How to Succeed in Nomenclature
- How to Succeed in Reactions and Synthesis
- How to Succeed in Mechanisms
By the time a student has finished this course, he or she should be able to simply look at a molecule and be able to predict how it will behave: Will it be soluble or insoluble in water or organic solvents? Is it an acid or a base? A nucleophile or an electrophile? How will it react? In order to do this, you will learn about molecular three-dimensional structure and bonding. The most important question in chemistry is, "Where are the electrons?" If you understand where electron density is located in three-dimensional space around a molecule, then you will be able to predict how that molecule will behave under various conditions. Predicting physical and chemical properties based on a few fundamental principles is vastly easier than trying to memorize everything without understanding what is going on.
In order for chemists to communicate with one another about organic molecules, and to have some way to list and categorize them in tables of reference, each organic structure must have a unique name, and vice versa. While this may seem a daunting task, it really is the simplest part of organic chemistry. It takes only a handful of rules to name even very complex organic molecules.
At the heart of organic chemistry are the reactions that transform one kind of molecule into another, or build larger molecules from smaller ones. These "tools" of organic chemistry are nothing more than the reactants that bring about these transformations. By the time you finish this course you will have a large "tool kit" of reactions with which to devise rather complex schemes for making a desired product out of a given starting material.
By far the most important pointof this class is organic synthesis, that is, making molecules. With your toolkit of reactions mentioned above, you will be able to start with simple, commercially available starting materials and transform them into complex molecules through a series of reactions. This is where critical thinking becomes essential. Not only will you have to know a large number of reactions, but you will have to be able to analyze the synthesis problem, and from a multitude of possible solutions, apply your knowledge to come up with the best one.
A mechanism is a detailed, step-by-step description of how a reaction occurs. All mechanisms are based on a very few, but critically important concepts: atomic properties, bonding, structure, acid-base reactions, thermodynamics, and kinetics. Mechanisms are important because they provide the detailed understanding that allows you to predict what reactions occur. Mechanisms cannot be memorized! They must be constructed based on those few principles mentioned. You must understand what's going on in a reaction to describe its mechanism.
Your toolkit will eventually contain literally hundreds of reactions. This is too much to simply memorize! Most of the seemingly diverse reactions you will learn can be grouped into a relatively few mechanistic patterns. This will help in remembering all of these reactions.
There are several concepts from General Chemistry that we will assume you have learned and learned well. While we will review all of them in this class, the reviews will be rather brief. It is absolutely essential that you have a solid understanding of these concepts. If you don't, you had best go back and review them.
You should know about atomic orbitals and electron configurations, and about periodic trends, especially that of electronegativity. (But we make it easy in Organic Chemistry. We work mostly with carbon, hydrogen, nitrogen, oxygen, the halogens, and a metal or two, and can pretty much forget about the rest of the periodic table!)
The principles of covalent and ionic bonding, hybrid atomic orbitals, and molecular geometries are absolutely essential to understanding the behavior of organic molecules. Probably the three most important things are Lewis structures, Lewis structures, and Lewis structures. The fourth most important thing is formal charge. If you cannot draw the correct Lewis structure for a molecule (with the correct formal charges), then you cannot make any correct predictions about its physical or chemical properties.
Combining electronegativities of atoms in a molecule with its molecular geometry allows one to predict the molecular polarity, which is an essential step in predicting physical and chemical properties of organic molecules.
Almost every single reaction in organic chemistry can be described in terms of an acid-base reaction, either by the Brönsted definition or by the Lewis definition. (The latter being far more common and important.) Also important is the concept of conjugate acids and bases and their relative strengths (weaker acid means stronger conjugate base, etc.) Know these concepts like the back of your hand!
To understand organic reactions and mechanisms, we make extensive use of the principles of equilibrium (including Le Châtelier's principle), thermodynamics, and kinetics. Unlike General Chemistry, though, we do very little mathematics in Organic Chemistry. Rather, we are more often concerned with qualitative relationships between these principles, and we make extensive use of reaction coordinate diagrams to describe them. Be able to read, interpret, and draw reaction coordinate diagrams (also called potential energy diagrams).
I can't emphasize enough the importance of knowing the key principles learned in General Chemistry: atomic trends, bonding, geometry, electronegativity, and most importantly, Lewis structures, Lewis structures, Lewis structures. And don't forget formal charges. Resonance structures are important too, but they are still Lewis structures. We'll spend a fair amount of time on them. With these principles firmly in hand, you can make predictions about the physical and chemical properties of organic molecules.
The other aspect of structure which will be relatively new to you will be that of stereochemistry. You may have had an introduction to it in General Chemistry, but in this course it will be substantially more important. If reactions are the meat of organic chemistry, then stereochemistry is the potatoes. You will need to be able to look at a two-dimensional drawing of a molecule and see it in three dimensions, possibly even rotate it in your mind about one or more of its axes, determine its absolute configuration, compare it to another structure, redraw it in two-dimensions again, and so on. Many students have a very difficult time with this, and for many of you it will be absolutely necessary to work with molecular models. With enough practice, you will be able make the transition between two-dimensional drawings and three-dimensional objects. But again, the key word is practice. I always allow students to bring their molecular models to quizzes and exams, but if you can do the problems without them, so much the better.
As mentioned earlier, nomenclature is probably the easiest part of organic chemistry. But a note of caution is in order: Since this does seem to be the simplest part, students often do not put in the necessary effort to master it. Like everything else, it still takes practice, practice, practice... and more practice. There is a particularly good computer program in the SLC for practice with organic nomenclature.
Trust me, this is the hardest part of organic chemistry. You are going to have to know one heck of a lot of reactions and be able to apply them to new situations. Memorization is not enough. You must be able to look at a synthesis problem, analyze it, and determine the best sequence of steps to carry it out. You will need to know all of the reactions that will produce a certain type of compound, and all of the reactions that that compound can undergo.
The best way to do this is to construct a "roadmap" that shows all of the different types of molecules we study, and what reactions are used to interconvert them. This roadmap can take various forms - it can be a simple outline, or an actual map, for example, showing all the types of organic molecules with arrows between them and the appropriate reagents and/or reaction conditions, paying particular attention to regiochemistry and stereochemistry. The important thing is that you make one, keep it up to date, and learn it.
When you approach a problem on a quiz or exam, you should be able to recall this roadmap in your head, and be able to choose the reaction or series of reactions needed to carry out some synthesis. Again, while there is going to be some memorization involved, you also have to understand how to look at a molecule, determine how it will behave with a given reactant, and what the product will be. This is where a thorough understanding of mechanisms comes into play. Most of the reactions in your toolbox can be categorized into a relative small number of mechanistic types. If you understand how the reactions work, it makes it easier to remember all of them.
You will know you are on the right track if the homework and reading start to become intuitive and logical, not just more details to memorize.
First and foremost, again, are Lewis structures, Lewis structures, Lewis structures. And formal charges. (Are you getting tired of hearing this yet?) Second is this: We use curved arrows in mechanisms to show the movement of electrons. Only, only, only!!! Curved arrows show movements of electrons, not atoms, not nothin' else. So, if you can draw the correct Lewis structure, get the formal charges right, understand electronegativity, relative acidity and basicity, thermodynamics, kinetics, and equilibria, then you can be assured that mechanisms will come easy. If you can't do these things, I can guarantee you'll be lost. Again, you cannot memorize mechanisms. Every new problem is a different situation. You have to understand mechanisms.