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Organic Chemistry, 6 edition



Organic Chemistry, 6 edition

Author: Marc Loudon and Jim Parise

Publisher: W. H. Freeman

Genres:

Publish Date: July 1, 2015

ISBN-10: 1936221349

Pages: 1648

File Type: PDF

Language: English

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Book Preface

A PREVIEW of THE SIxTH EDITIoN

We believe, and research in chemical education shows, that students who make the effort to learn but still have trouble in organic  chemistry are in many cases trying to memorize their way through the subject. One of the keys to students’ success, then, is to provide them with help in relating one part of the subject to the next—to help them see how various reactions that seem very different are tied together by certain fundamentals. An overarching goal of our text is to help students achieve a relational understanding of organic chemistry. Here are some of the ways that we have tried to help students meet this goal.

Use of an Acid–Base Framework Is a Key to Understanding Mechanisms

Although we have organized Organic Chemistry, Sixth Edition, by functional group, we have used mechanistic reasoning to help students understand the “why” of reactions. Mechanisms alone, however, do not provide the relational understanding that students need. Left to their own devices, many students view mechanisms as something else to memorize, and they are baffled by the “curved-arrow” notation. We believe that an understanding of acid–base chemistry is the key that can unlock the door to a mechanistic understanding of much organic chemistry. We use both Lewis acids and bases and Brønsted acids and bases as the foundations for mechanistic reasoning. Although students have memorized the appropriate definitions in general chemistry, few have developed real insight about the implications of these concepts for a broader range of chemistry. We have dedicated Chapter 3 to these fundamental acid–base concepts. The terms “nucleophile,” “electrophile,” and “leaving group” then spring easily from Lewis and Brønsted acid–base concepts, and the curved-arrow notation makes sense. We have provided a substantial number of drill problems to test how well students have mastered these principles. We have reinforced these ideas repeatedly with each new reaction type. We also cover free-radical reactions, but not until the electron-pair concepts are fully established.

Tiered Topic Development Provides Reinforcement of Important Ideas

We have introduced complex subjects in “tiers.” In other words, students will see many concepts introduced initially in a fairly simple way, then reviewed with another layer of complexity added, and later reviewed again at a greater level of sophistication. Acid–base chemistry is an example of tiered development. After the initial chapter on acid–base chemistry and the curved-arrow notation, these concepts are revisited in detail as they are used in the early examples of reactions and mechanisms, and again with the introduction of each new reaction type.

The presentation of stereochemistry is another example of the tiered approach. The concept of stereoisomerism is introduced in Chapter 4 (Alkenes). A full chapter on stereochemistry comes two chapters later. Cyclic compounds and the stereochemistry of reactions follow in the next chapter. Then the ideas of group equivalence and nonequivalence are introduced even later, both in the context of enzyme catalysis (Chapter 10) and NMR spectroscopy (Chapter 13).

The approach to organic synthesis is yet another example. We start with simple reactions and then show students how to think about them retrosynthetically. Then, later, we introduce the idea of multistep synthesis using relatively simple two- and three-step sequences. Later still, we have another discussion in which stereochemistry comes into play. Even later, the use of protecting groups is introduced.

Another example is the presentation of resonance. We begin in Chapter 1 with resonance as a simple explanation for hybrid structures. Then, in Chapter 3, students learn to derive resonance structures with the curved-arrow notation, and they learn that resonance has implications for stability. In Chapter 15, the whole issue of resonance is reviewed and the justification of resonance with molecular orbital theory is presented.

This tiered presentation of key topics requires some repetition. Although the repetition of key points might be considered inefficient, we believe that it is crucial to the learning process. It is tempting for the instructor to cover every aspect of a topic when introducing it for the first time. However, in our experience, some students are easily overwhelmed by single, comprehensive presentations. Education research has proven that when material is revisited frequently, with new details being added each time, learning is enhanced and concepts are internalized. When a topic is considered after its first introduction, we have provided detailed cross-referencing to the original material. Students are never cast adrift with terminology that has not been completely defined and reinforced.


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