It’s My Favorite Time of the Year! Chapters 6 and 7

It’s my favorite time of the year. Finally, we get to do chemistry in organic chemistry! Not to malign BDE, IMF, chair vs. boat conformations, etc., but I have always thought of the stuff leading up to this point—strains and conformers, the designation of stereochemistry and the terms and rules associated with their nomenclature—a bit of a molecular card game. Though important, it’s just a bunch of rules, names, and designations so chemists can speak with other chemists. Chapters 6 and 7 introduce students to real applications of chemistry. It seems like a lot of information to throw at them but it works well.

Karty’s elegant introduction to acid/base chemistry in Chapter 6 (“The Proton Transfer Reaction”) is a great way to ease into synthesis. Curved arrow notation is presented so that students do NOT have to memorize endless reactions. Negatives go to positives. Push the electrons to something that would “like” electrons. Students who prove this to themselves are almost giddy with the simplicity of it all. Acid/base chemistry is the first real memory that many students have from general chemistry and, unfortunately, it is a very polarizing topic. Students either love Henderson Hasselbalch and the comfort that an equation gives them or hate the wave of the hands to get an answer that is almost equally as baffling with its pKa’s and pH’s. Karty’s coverage in terms of products and reactants gives all students a nice review without getting overwhelming.

The segue into pKa’s brings students to Table 6-1 (below). The table is brief which really emphasizes that the actual pKa for a proton doesn’t need to be precise, just close. Protonation constitutes the first step in so many reactions but it can be so overwhelming for even the more experienced student. When do I need a proton? Which atom protonates first? How do you know to protonate that one?! Answers to these questions become more obvious and can be systematically thought through with this pKa table.

Table 6-1

Chapter 6 also helps clear up misconceptions about reaction products. When students see a reaction such as

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they often are of the mindset that the one molecule reacts with the one other molecule to produce one molecule of something else. Major products, minor products and side products seem incomprehensible. Karty’s brief discussion of the leveling effect shows them there are often multiple possible reactions, even in acid/base chemistry.

By ending this chapter with amino acids, students see that there are many molecules with more than one functional group and that they work dependently (inductive effects) and independently (pKa’s of the amine, carboxylic acid and the side chain).

In Chapter 7, Karty’s summary of the most common elementary steps reinforces curved arrow notation and the pKa concepts. Looking at every organic reaction beyond coordination as a substitution, an elimination, an addition, or a rearrangement reaction again helps students think instead of memorize. The detailed reaction mechanisms at the end of the chapter let students see how to do approach a problem instead of just scribbling down the mechanism that the instructor comes up with—they are a great conversation starter! First steps now seem very obvious (protonate something!) and reaction pathways can be predicted with the knowledge of acid/base chemistry (in the Lewis sense). Students ask if their proposed mechanism is viable; could they do this instead of that? By reflecting on the conditions, they can come up with feasible alternate mechanistic routes. They can actually determine what is a reasonable mechanism based on conditions and Lewis acid/base chemistry.

Chapter 7 is a great introduction to all the possible reactions. Taking Karty’s lead, I’ve decided to lay a foundation of the common reactions. Rather than just go in chapter order, I am now including parts of chapters 8, 11, 17 and 21. The text is well set up for this tour. Next semester, I will revisit, reinforce, and add new twists to these concepts.

-Rita Majerle, Hamline University

Click here to learn more about Prof. Majerle

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