This is the first in a series of posts answering some frequently asked questions about the third edition of Joel Karty’s Organic Chemistry: Principles and Mechanisms
. This section covers topics up to chapter 7, typically taught in the first semester. If you have any unanswered questions please ask them in the comments below.
Why is Chapter 1 not a “general chemistry review” chapter?
General chemistry review topics are spread throughout the first six chapters of my book to provide a better transition from general chemistry to organic chemistry. Students tend not to have retained as much general chemistry as we want or need them to have retained, in which case a general chemistry review chapter, which marches rapidly through several topics, ends up leaving students behind. Moreover, even if a student is quite capable with general chemistry topics, it does not necessarily mean that the student is able to apply those concepts to organic molecules, which are larger and more complex than molecules students encounter in general chemistry.
By spreading general chemistry topics throughout the first six chapters, my textbook allows students more time to spend on a particular topic before moving on to the next. Once a general chemistry topic is reviewed, students then see how it applies to organic chemistry, in ways beyond what they would have seen in general chemistry. For example, in Section 1.5, students quickly review the rules for drawing Lewis structures of small molecules. Then, in Section 1.6, students learn how to complete Lewis structures for large, complex organic molecules. As another example, in Section 6.4, students review Gibbs free energy and energy diagrams, and then in Section 6.6, students learn how to use free energy diagrams and charge stability to predict relative strengths of acids and bases.
Why does resonance appear in Chapter 1?
Resonance appears in Chapter 1 to give students as much practice with predicting molecular stability and drawing curved arrows as possible before they are held accountable for working with reactions and mechanisms. Practicing with resonance helps students understand and make predictions about key aspects of molecular stability, a major factor that dictates the outcome of a chemical reaction. Students also draw curved arrows when drawing resonance structures, the same curved arrows that are used in drawing mechanisms. Students are typically quite ready for working with resonance in Chapter 1 because it is it is a review topic from general chemistry and a straightforward extension of Lewis structures. When the introduction of resonance is instead delayed until the context of bonds and conjugation, students have less time to gain mastery of resonance and curved arrow notation before starting reactions and mechanisms, thus compromising the learning of reactions and mechanisms.
Why are protic and aprotic solvents introduced in Chapter 2?
Traditionally, protic and aprotic solvents are introduced in the context of the competition between SN1, SN2, E1, and E2 reactions, to demonstrate the way solvent effects can impact the outcome of that competition. When students learn a new concept like this in the context of predicting the outcome of a reaction, students tend to focus on just the reaction, not the understanding of the next concept. In such cases, the understanding of solvent effects falls by the wayside. With my textbook introducing protic and aprotic solvents in Chapter 2, students learn the concept in the context of a topic that is already familiar to them from general chemistry: solubility. Not only does this make it more comfortable for students to focus on understanding protic and aprotic solvents when they first learn the topic, but students will see it a second time when they later learn about the SN1/SN2/E1/E2 competition. This makes it more manageable for students to focus on the SN1/SN2/E1/E2 competition then.
Why is Molecular Orbital Theory presented separately from Valence Bond Theory in Chapter 3?
In many textbooks, molecular orbital theory and valence bond theory are presented together and rapidly, often in a general chemistry review chapter. As a result, students tend to come away with substantial confusion as to what actually distinguishes the two theories, and what the advantages and disadvantages are to each. In my textbook, Chapter 3 is devoted entirely to these two theories. Chapter 3 first develops valence bond theory, applying it toward the structure and stability of common small molecules. Then, those ideas are revisited from the perspective of molecular orbital theory. This helps students to better distinguish one theory from the other, and to better come away with the notion that valence bond theory is simpler, at the expense of having significant limitations.
Moreover, molecular orbital theory is presented entirely in a “Deeper Look” section. All “Deeper Look” sections are devoted to topics that are more challenging or more quantitative. Therefore, instructors can teach as much or little molecular orbital theory as they see fit for their students, without worrying about being bitten later on by skipping its coverage.
In Chapter 4, why are conformers covered before constitutional isomers?
The main reason is for students to come away with a better understanding of why some molecules that might initially appear to be different, such as the ones below, are in fact not constitutional isomers. We can show students how to make this conclusion from a process we give them, but it helps even more so to show students that they are in fact the same molecule through single bond rotations.
That having been said, an instructor who wishes to teach constitutional isomers before conformers can do so seamlessly, simply by teaching Sections 4.10 – 4.13 before Sections 4.1 – 4.9. In fact, some users of the textbook already teach in this rearranged order.
Why are chirality and configurational isomers introduced before reactions?
Some textbooks introduce chirality and configurational isomers after the first organic reactions and mechanisms have been introduced. When a new concept is introduced in the context of reactions, students tend to focus on the outcome of the reaction rather on understanding the new concept. In my textbook, I begin to introduce reactions and mechanisms in Chapters 6 and 7, thus allowing students to focus entirely on chirality and configurational isomers in Chapter 5, without distraction. This gives students at least two chapters’ worth of time to master chirality and configurational isomers before learning about stereochemistry of reactions in Chapter 8.
Why is curved arrow notation for reactions introduced in Chapter 6 in the context of proton transfer reactions?
Some textbooks introduce curved arrow notation for reactions in the context of organic reactions that are new to students, such as alkene additions. In such cases, students will already have their hands full with learning about electrophiles and carbocation intermediates, and their focus on understanding curved arrow notation will be compromised. In my textbook, curved arrow notation for reactions is introduced in the context of proton transfer reactions, which are already familiar to students from general chemistry. Students will already be familiar with acids and bases, and the bonding changes that occur in these reactions, thus allowing students to focus more wholly on curved arrow notation.
Why are reaction free energy diagrams introduced in Chapter 6 in the context of proton transfer reactions?
Some textbooks introduce reaction free energy diagrams in the context of organic reactions that are new to students, such as alkene additions. In such cases, students will already have their hands full with learning about electrophiles and carbocation intermediates, and their focus on understanding how to construct or interpret free energy diagrams will be compromised. In my textbook, reaction free energy diagrams are introduced in the context of proton transfer reactions, which are already familiar to students from general chemistry. Students will already be familiar with acids and bases, and the bonding changes that occur in these reactions, thus allowing students to focus more wholly on understanding reaction free energy diagrams.
Can I skip Chapter 7 (An Overview of the Most Common Elementary Steps), because the topics will be revisited later in the book in the context of the reactions where they apply?
Although it might be tempting to skip Chapter 7 for that reason, Chapter 7 is important to cover/teach, for two main reasons.
First, Chapter 7 allows students to focus on learning key aspects of elementary steps and curved arrow notation before being held accountable for predicting products of reactions with multistep mechanisms. In other textbooks, where elementary steps are introduced alongside reactions with multistep mechanisms, students’ focus is pulled toward predicting the overall products, at the expense of understanding mechanisms. This is a major cause for memorization. With Chapter 7, students can focus on elementary steps in what is essentially a risk-free environment.
Second, messaging. As experts, we know that mechanisms simplify organic chemistry. We tell students that this simplicity comes from a small number of elementary steps appearing over and over in hundreds of seemingly different reactions. Students are being asked to take this on faith when we tell it to them at the outset, before they can see what those elementary steps actually are, or how simple each step is. With all of these common elementary steps shown together, upfront, students can gain assurance that the various elementary steps are straightforward and manageable. And knowing that all of the reactions mechanisms encountered through Chapter 25 will be constructed from the same 10 elementary steps, students can come away with the belief that elementary steps and mechanisms actually do simplify organic chemistry, even before they see the first multistep mechanism. Students come away with the belief that spending time on elementary steps and mechanisms is worthwhile.
-Joel Karty, Elon University
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