Electron Flow in Organic Chemistry: A Decision-Based Guide to Organic Mechanisms 2nd Edition

Book Preface

TO THE STUDENT

Critical Thinking Approach

Organic chemistry courses have a well-deserved reputation for being highly memorization based. But it does not have to be so. An organic chemistry course is a great place to learn critical thinking. My students kept asking me, “Why didn’t it do this instead of that?” Soon I was mapping out alternatives and getting them to decide the answers to those questions. My course had evolved from “know the answer” to “explain the answer,” and also “predict what would happen here.” As the course progressed, my students developed a good chemical intuition and felt they understood why reactions occurred. They could write reasonable mechanisms for unfamiliar reactions and predict what might happen for reactions they had never seen. How to learn organic chemistry by using this critical thinking approach is the essence of this book.

Dealing with Informational Overload

Ideally, college is where you learn to think, but there is often so much factual material to cover in an organic chemistry course that memorization can take over. In the face of the sheer mass of content to be learned, the development of the necessary skills critical to becoming a scientist—logic and analysis—can be lost. This “tyranny of content” in an ever-growing field means that the “why” of the field may get swamped under a flood of facts. The mystery of a good puzzle, the draw of the sciences, can also be lost.

You might approach organic chemistry with the idea that only memorization can get you through it; this may have been true many years ago, but it is not the case now. With memorization, if you have not seen it before, you are usually in trouble. Information learned through memorization is also the first to be forgotten, and the volumes of information required in organic chemistry seem to be lost particularly rapidly. This loss can even occur before the cumulative second semester final.

An Expert Systems Approach to Organic Chemistry

To “explain the answer,” you need to know what the alternatives are, and why one of them succeeds and others fail. You need to “generate and select” alternatives, which is the essence of a good critical thinking process. The map of all alternatives from the start point can be represented as a tree, and is our “problem space.” You need an efficient way to navigate this problem space to the correct answer. For that, you need a small set of essential principles, or “control knowledge,” to guide the route selection decisions toward the correct answer. Good intuition arises from the automatic use of control knowledge to guide the decision process.

The impressive advantage that a decision-based approach to organic chemistry has over memorization is that it engages you in critical thinking, a skill everyone can benefit from improving. This approach allows for extrapolation into the unknown and provides room for the joy of discovery. If you are going to learn how to think in organic chemistry, you need to know what the alternative paths are and how to decide between them.

The development of decision-making algorithms for artificial intelligence systems has led to a new way of thinking about the decision process. Computers have to make use of decision trees and problem spaces, where all possible choices are examined and weighed and the best of the options selected. This same methodology can be applied to organic chemistry. You will have to learn about problem spaces, search trees, and methods to decide the best path. This text extracts the essence of the field: the conceptual tools, the general rules, the trends, the modes of analysis, and everything that one would use to construct an expert system. It explains and makes use of analysis tools more common to expert systems, but rare in undergraduate organic chemistry texts. If you can internalize this expert-system decision process, you will develop a chemical intuition and are well on your way to becoming an expert yourself.

Unique to This Text

This book organizes reactions by similar processes, as you would in an expert system. Reactants are grouped into generic groups that behave similarly. By being able to classify hundreds of different structural types into a small number of electron sources and sinks, you take control of the information overload and make it manageable. You will be able to make a good guess at how new reaction partners might behave.

All mechanisms are viewed as composed of simple elemental processes, the electron flow paths. Even the most complex reactions can be simplified into a sequence of basic electron flow paths. These elemental processes are limited in number and are repeated, again and again, making them easier to both learn and retain. In this way, a mere dozen electron flow paths can explain nearly all of the common reactions found in an undergraduate organic course. This decision-based book shows how to choose which of the dozen common electron flow paths are reasonable to use, and in what order. New reactions become puzzles to solve, not just another item to be memorized. Reactions are much easier to remember if you can understand how they work.

Motivation and Relevance

The most important question that you as a student have to answer is, “Why am I in this course?” Organic chemistry is a lot of work no matter what approach is used, and you will need to see the personal relevance in order to have the motivation to succeed. Premedical students need the ability to reason through complex problems; this is the essence of diagnosis. Biology majors need to have a good chemical intuition, so that they can understand the chemistry of life, what makes it work or malfunction. A good organic chemistry course will give you precisely these skills: good chemical intuition and the ability to approach and solve complex problems. Rote memorization will provide neither. The critical thinking skills and methods of analysis learned in a decision-based organic course are highly valuable and easily transportable to other areas.