Consider what the novice sees when they begin a new functional group chapter. In an alcohols chapter, for example, students first learn how to recognize and name alcohols, then they study the physical properties of alcohols. Next, students might spend time on special spectroscopic characteristics of alcohols, after which they learn various routes that can be used to synthesize alcohols from other species. Finally, students move into the heart of the chapter: new reactions that alcohols undergo and the mechanisms that describe them. Within a particular functional group chapter students find themselves bouncing among several themes.
Even within the discussion of new reactions and mechanisms a particular functional group can undergo, students are typically faced with widely varying reaction types and mechanisms. Take again the example of alcohols. Students learn that alcohols can act as an acid or as a base; alcohols can act as nucleophiles to attack a saturated carbon in a substitution reaction, or to attack the carbon atom of a polar bond in a nucleophilic addition reaction; protonated alcohols can act as electrophiles in an elimination reaction; and alcohols can undergo oxidation, too.
With the substantial jumping around that takes place within a particular functional group chapter, it is easy to see how students can become overwhelmed. Under a functional group organization, students don’t receive intrinsic and clear guidance as to what they should focus on, not only within a particular functional group chapter, but also from one chapter to the next. Without clear guidance, and without substantial time for focus, students often see no choice but to memorize. And they will memorize what they perceive to be most important—predicting products of reactions, typically ignoring, or giving short shrift to, fundamental concepts and mechanisms.
Under the mechanistic organization in this book, students experience a coherent story of chemical reactivity. The story begins with molecular structure and energetics, and then guides students into reaction mechanisms through a few transitional chapters. Thereafter, students study how and why reactions take place as they do, focusing on one type of mechanism at a time. Ultimately, students learn how to intuitively use reactions in synthesis. In this manner, students have clear and consistent guidance as to what their focus should be on, both within a single chapter and throughout the entire book.
The patterns we, as experts, see become clear to students when they learn under this mechanistic organization. Consider the following four mechanisms:
The mechanism in P-1 is for a Williamson synthesis of an ether; the one in P-2 is for an alkylation of a terminal alkyne; the one in P-3 is for an alkylation of a ketone; and the one in P 4 is for the conversion of a carboxylic acid to a methyl ester. In these four reactions, the reactants are an alcohol, an alkyne, a ketone, and a carboxylic acid. In a functional group organization, these reactions will be taught in four separate chapters. Because all four reaction mechanisms are identical—a deprotonation followed by an SN2 step—all four reactions are taught in the same chapter in this book: Chapter 10.
Seeing these patterns early, students more naturally embrace mechanisms and use them when solving problems. Moreover, as students begin to see such patterns unfold in one chapter, they develop a better toolbox of mechanisms to draw upon in subsequent chapters. Ultimately, students gain confidence in using mechanisms to predict what will happen and why. I believe this is vital to their success throughout the course and later on admission exams such as the MCAT.
-Joel Karty, Author of Organic Chemistry: Principles and Mechanisms