Other organic chemistry textbooks devote their first chapter to reviewing general chemistry, speeding through the highlights of what students ought to have retained from their general chemistry course. I take a different approach in my book. Instead, I spread the bulk of these general chemistry review topics over the first four chapters—chapters that are devoted to various aspects of molecular structure and stability. Therefore, in many instances throughout these chapters, students will review familiar material from general chemistry and will almost immediately apply it to a new organic chemistry topic. There are at least three advantages to this: (1) students better see organic chemistry as an extension of topics from general chemistry, rather than being distinct from general chemistry, so the transition to organic chemistry is more seamless; (2) because the review topics are split up, they can be covered more extensively, if necessary, without the instructor or students feeling bogged down in a lengthy rehash of general chemistry; and (3) students can better hit the ground running at the outset of the course, delving into organic chemistry topics earlier.
Because the first four chapters have extended coverage of a number of general chemistry topics, you can feel comfortable spending less time on several of those topics in class, or even requiring students to review them on their own outside of class. Well before the course begins, I encourage you to identify the specific topics/sections to cover only lightly in class or exclude from class time entirely. You will appreciate the time saved to devote to other topics later on. In my case, I spend roughly three weeks on Chapters 1-4, which I view as a week saved.
By the same token, there are topics/sections in the first four chapters on which I strongly recommend spending a good amount of time in class. These are topics that students either don’t learn well in general chemistry, are very important foundations for later material, or both. Here I have listed these sections, and I have provided rationale.
1.6. Strategies for Success: Drawing Lewis Dot Structures
o Students are generally good at using the stepwise protocol for
drawing Lewis structures of small, inorganic molecules. Organic
molecules, however, are often much larger and are more structurally
complex, rendering that stepwise protocol ineffective. Section 1.6
gets students accustomed to applying common bonding scenarios to
organic molecules (e.g., four bonds to C, three bonds and a lone pair
to N, etc.), so working with organic molecules is far less
1.9. Assigning Electrons to Atoms in Molecules: Formal
o Formal charge is vastly important in organic chemistry, especially in
mechanisms where formal charges are located on different atoms from
one step to the next. Students learn formal charge in general
chemistry, but often don’t retain it because they memorized the
equation to calculate formal charge. In Section 1.9, formal charge is
taught in a way that is more intuitive, asking students to compare
the number of electrons assigned to an atom in a molecule to the
number of electrons the isolated atom has. Thus, students better
retain their ability to calculate formal charge.
1.10. Resonance Theory; 1.11. Strategies for Success: Drawing
All Resonance Structures
o Resonance is typically covered in general chemistry, but I have yet
to see a student entering organic chemistry already having mastery of
the topic. At best, students have a vague recollection of what
resonance structures are and what a resonance hybrid is. At the same
time, resonance is vital to understanding aspects of molecular
structure and chemical reactivity.
o Section 1.10 provides the principles of resonance theory, and Section
1.11 gives students the tools to draw resonance structures. In
Section 1.11, in particular, students are taught to look for one of
four basic features appearing in a Lewis structure, to then add the
appropriate curved arrows based on that feature, and finally to
follow the curved arrows they drew to arrive at the next resonance
structure. Teaching students to draw resonance structures by first
identifying one of these four features has been very effective in my
o More than just serving as a model to understand molecular structure
and chemical reactivity, aspects of resonance prepare students
extremely well for working with mechanisms. The curved arrow notation
that students work with in Section 1.11 is precisely the same curved
arrow notation used in reaction mechanisms. Moreover, when drawing
resonance structures, atoms can gain and lose octets, and formal
charges “hop” from one atom to another, in much the same way we see
these things happen in mechanisms. Working with mechanisms,
therefore, does a great job identifying deficiencies students have
with formal charges and octets. Some textbooks delay an in-depth
treatment of resonance until after conjugation has been taught, but
because resonance provides such a good preparation for mechanisms, I
strongly believe that delaying resonance like this does students a
great disservice. To the contrary, the earlier resonance is presented
and the more frequently it is revisited, the better experience
students will have throughout the course.
1.12. Shorthand Notations
o One reason to spend time on this section is that line structures are
new to most students. Moreover, line structures demand students to be
proficient with octets and formal charges, so, like resonance, line
structures do a great job identifying deficiencies in these areas.
o Along those lines, I strongly recommend heavily emphasizing to your
students to become intimately familiar with the bonding scenarios in
Table 1-5. The earlier that students can instantly associate an
atom’s formal charge with the number of bonds and lone pairs the atom
has, the more competent and confident students will be.
1.13. An Overview of Organic Compounds: Functional
o Students of course need to know functional groups because functional
groups dictate physical and chemical behavior and are the basis for
nomenclature. It is important for students to begin to learn certain
functional groups and their corresponding compound classes here for a
couple reasons: (1) Interchapter A, the first unit on nomenclature,
appears immediately after Chapter 1; and (2) students begin to
associate functional groups with physical properties in Chapter 2 and
with chemical properties (acid strength) in Chapter 6.
2.3. Strategies for Success: The Molecular Modeling
o I am a strong believer in model kits, telling students that model
kits can do a lot of the hard work for them. This is especially true
when students work with conformations and chair flips (Chapter 4) and
stereochemistry (Chapter 5). But I also learned the hard way that
it’s insufficient to just tell students that model kits are helpful;
students must be shown. Without me bringing model kits into the
classroom, my students would convince themselves that model kits are
too time consuming to be worth it. My students would constantly look
for shortcuts to avoid model kits, to my students’ detriment. But
once I started bringing model kits into the classroom, even to carry
out simple exercises like the ones described in Section 2.3, I
started to get close to 100% buy-in by students, and this pays
dividends down the road.
o Students generally approach this topic from the standpoint of “like
dissolves like.” In truth, students can probably solve most
solubility problems without going any deeper than this. But it is
quite worthwhile to spend time on Section 2.7 in class, specifically
delving into the role that solvation plays in dissolving ionic
compounds. Beyond its application to solubility, solvation can have a
major impact on chemical reactions, especially SN1, SN2, E1 and E2
reactions (Chapter 9). In my experience, students deal much better
delving into solvation for the first time here—in a familiar context
of solubility—than in the throes of dealing with the SN1/SN2/E1/E2
2.8. Strategies for Success: Ranking Boiling Points and
Solubilities of Structurally Similar Compounds
o Earlier in this chapter, students reviewed how to rationalize
relative boiling points and solubilities by examining just one type
of intermolecular interaction. Section 2.8 asks students to recognize
all types of intermolecular interactions that are present, and then
to evaluate their relative importance. In so doing, this section does
a good job identifying deficiencies students might have with
identifying and assessing the relative importance of intermolecular
2.9. Protic and Aprotic Solvents
o Other textbooks typically introduce the topic of protic and aprotic
solvents for the first time in the context of the SN1/SN2/E1/E2
competition (Chapter 9 in my book), and you could consider delaying
Section 2.9 until then, but I strongly recommend against doing so.
The SN1/SN2/E1/E2 competition is not only unfamiliar to students, but
is also really challenging for many. Therefore, when students are
learning how to deal with the SN1/SN2/E1/E2 competition in Chapter 9,
it is better to invoke protic and aprotic solvents as a review rather
than as an entirely new concept. By contrast, here in Section 2.9,
students learn about protic and aprotic solvents in the familiar
context of solubility.
3.1 – 3.8. Atomic and Molecular Orbitals; Hybridization;
Valence Bond Theory; Orbital Pictures and Orbital Energy
o I tend to slow down a bit on these sections to cover them in good
depth, for a couple reasons. (1) My students don’t tend to retain
much of this material from general chemistry; and (2) it helps
prepare students for conjugation and aromaticity in Chapter 14 and
UV-vis spectroscopy in Chapter 15. To save time, however, you can
consider shortening most of the topics in these sections without
compromising material that comes later in the book. The exception is
Section 3.4 on hybridization. I would make sure to cover that section
to good depth because of the frequency with which hybridization is
used to explain important aspects of reactions throughout the book.
3.9. Bond Rotation about Single and Double Bonds: Cis and
o The idea that single bonds rotation but double bonds do not is
relatively straightforward, but I spend time in class on this topic
for two reasons. (1) It’s a nice transition into a major topic of
Chapter 4—conformers. (2) Discerning which double bonds have
available cis/trans configurations is more challenging to students
than we might guess. Therefore, I have found that taking students
through the exercise of determining whether a double bond has
cis/trans configurations highlights deficiencies that students might
have with manipulating molecules in three dimensions.
3.11. Hybridization, Bond Characteristics, and Effective
o These topics have important implications in chemical reactivity,
especially regarding acid strengths (terminal alkynes) and
heterolytic bond dissociation to produce carbocations (SN1 and E1
reactions). You could consider delaying this topic until Chapter 6,
where effective electronegativity is applied to acid strengths, but I
recommend against doing so. In Chapter 6, students will need to focus
on curved arrow notation, acid-base equilibria, reaction coordinate
diagrams, and charge stability, so it is better there to invoke
effective electronegativity as review than as a new concept.
4.1-4.9. Conformational Analysis, Ring Strain, and Chair Flips
o These sections are all rather standard, and I slow down to cover them
in good depth. To save time, however, I gloss over Section 4.4
(Conformers: Cyclic Alkanes and Ring Strain) in class, quickly
mentioning the results of Table 4-1 and highlighting the fact that 6-
membered rings are strain free, 5- and 7-membered rings have mild
strain, and 3- and 4-membered rings are highly strained. I leave the
relationship between ring strain and heat of combustion for out-of-
class exercises. I also save time in class by glossing over Sections
4.5 (Conformers: The Most Stable Conformations of Cyclohexane,
Cyclopentane, Cyclobutane, and Cyclopropane) and 4.6 (Conformers:
Cyclopentane, Cyclohexane, Pseudorotation, and Chair Flips), slowing
down in Section 4.5 just to cover cyclohexane’s chair conformation,
and slowing down in Section 4.6 to cover the basics of cyclohexane
o I also take time in class to go through the exercise from Section
4.7. Strategies for Success: Drawing Chair Conformations of
Cyclohexane. I demonstrate once how to draw an accurate chair
conformation, and then tell students that they must practice that
exercise repeatedly. I also take this opportunity in class to show
students a few ways of drawing a chair conformation inaccurately—e.g,
equatorial bonds that should point left are drawn pointing right, and
vice versa; and bonds that are not clearly axial or equatorial.
4.10. Strategies for Success: Molecular Model Kits and Chair Flips
o I emphasize this section heavily in class, as this is where model
kits become really useful for students. Without model kits, students
try to make associations of the sort “if I see X, and Y takes place,
then I should draw Z.” It’s a form of memorization. But with model
kits, students build the model based on what they see drawn,
manipulate the model including chair flips, make their assessments
based on sterics, and then use the resulting model as a guide to draw
the result. When model kits are used in this way, students are more
accurate in their answers, and they come away with a better feel for
the chemistry at play. Getting student buy-in to use model kits
regularly like this, however, is partly an outcome of the earlier
emphasis I place on model kits from Sections 2.3 and 3.10.
4.11. Constitutional Isomerism: Identifying Constitutional Isomers
o Even though my students dealt with constitution isomers in general
chemistry, I spend significant time on this material in class because
most of my students don’t have a sufficient grasp connectivity when
they enter the course. Yet being able to recognize differences in
connectivity is important for later topics, such as identifying
stereocenters and dealing with regiochemistry.
4.12. Constitutional Isomers: Index of Hydrogen Deficiency (Degree of Unsaturation)
o This material is new to most students, and is a standard topic.
However, I present it differently in my book than in other books.
Other books coach students to use a formula to calculate the IHD of a
given formula. My book asks students to quickly sketch a molecule
saturated molecule with the same number of non-hydrogen atoms given
in the formula, and compare the number of hydrogen in the given
formula to the number of hydrogen atoms in the saturated molecule.
This takes a few seconds longer than plugging numbers into a formula,
but students remember this process better than a formula they try to
commit to memory, so their answers are more accurate. That being
said, my book does present the 2n + 2 result for saturated
hydrocarbons, and it also gives students two in-chapter problems
(4.23 and 4.24) for students to determine how that results changes
with each added N, O and F atom.
4.13. Strategies for Success: Drawing All Constitutional Isomers of a Given Formula
o I spend time in class to teach this strategy, bringing students
through at least one example. Although drawing all constitutional
isomers may not be a vital task in itself, the protocol helps
students learn connectivity more deeply when they must consider the
next isomer to draw, and when they compare an isomer they just drew
to other isomers they previously drew. This exercise also helps
identify deficiencies that can pose problems for students later on;
students who struggle with drawing all isomers of a given formula
will more likely struggle with mechanisms, where it is important to
keep track of bonds broken and formed.
Nomenclature is divided into five interchapters (Interchapters A, B, C, E, and F) to give instructors flexibility as to how and when to teach the material. In my case, the only nomenclature I teach in class is Interchapter C, which deals with stereochemical configurations. I assign the other four nomenclature interchapters for self study. My students are held accountable, however, for all nomenclature material on exams.
To ensure that my students are actually working on the nomenclature I don’t cover in class, I assign copious nomenclature problems in Smartwork. I assign a large number of nomenclature problems there, even though I don’t cover the material in class, because of how straightforward nomenclature is to master: encounter a new rule, learn the rule, apply the rule, then repeat. The critical part here is applying the new rule, which the Smartwork problems enable my students to do.
I require my students to work through the nomenclature interchapters roughly where they appear in the book: following Chapters 1, 3, 5, 7, and 9. Therefore, my students complete all of nomenclature in the first semester. Another effective way to cover nomenclature is to save Interchapters E and F for second semester, so that students stay fresh with nomenclature throughout the entire year. Covering nomenclature in this way remains effective because Interchapters E and F deal with alcohols, amines, ketones, aldehydes, and carboxylic acids and their derivatives—compound classes whose reactions are principally covered in the second half of the textbook.
Chapter 6 deals with the introduction of mechanisms, thermodynamics, and charge stability in the context of proton transfers. Section 6.1 reminds students what a proton transfer is and introduces curved arrow notation as a means by which to keep track of bonds breaking and forming. I don’t spend much time on this section in class because students are familiar with acid-base reactions from general chemistry, and the curved arrow notation presented here is the same that students learned in the context of resonance in Chapter 1.
Section 6.2 deals with equilibria pertaining to proton transfer reactions. I only touch on the highlights of this material in class because much it is review from general chemistry. I do spend some significant class time on Section 6.2b (Predicting the Outcome of a Proton Transfer Reaction Using pKa Values) because it is a task that students must apply frequently throughout the rest of the course. I will also present a quick example from Section 6.2d (Le Châtelier’s Principle, pH, and Percent Dissociation) so students can later tackle the material in the biomolecules sections (Sections 6.9 and 6.10) dealing with ionization states of amino acids and electrophoresis.
Section 6.3 (Thermodynamics and Gibbs Free Energy), too, is largely a review of material students would have seen in general chemistry, but there are two key things that I make sure to get across in class. One is the association between higher free energy and less stability. The other is the meaning of the reaction coordinate. I spend significant class time on the reaction coordinate because, even though students in general chemistry see it appear as the label of the horizontal axis in free energy diagrams, students entering organic chemistry largely find the term mysterious and struggle to articulate what it actually means. Other textbooks take the reaction coordinate for granted, assuming that students know what it is and how to work with it, but my book does not; it is important for students to work comfortably with the reaction coordinate, especially as it pertains to identifying key features of a free energy diagram (such as intermediates) and applying the Hammond postulate.
Section 6.4 (Strategies for Success: Functional Groups and Acidity) is relatively straightforward, but it is a very important section. It applies for the first time the idea that functional groups dictate chemical reactivity, so it reinforces the need for students to recognize various functional groups. Thus, this section helps diagnose issues that students have with identifying functional groups. Section 6.4 also is the place where I tell students I need them to commit the pKa values for the following types of acids to memory: H2SO4; HCl, H3O+ and protonated alcohols; carboxylic acids; phenols; NH4+ and protonated amines; ketones and aldehydes; terminal alkynes; H2; NH3 and amines; alkenes and benzenes; alkanes and ethers. I ask students to know these pKa values so students are equipped to handle proton transfer steps as part of larger mechanisms later on. These pKa values are used regularly to justify when such a proton transfer makes sense, and whether it is reversible or irreversible.
Sections 6.5 and 6.6 develop the idea of charge stability using relative acid strengths. I devote about one-and-a-half class periods to this material because of how useful charge stability is in understanding mechanisms. Students need to be able to determine the relative stability of a charged species on the basis of its structure.
As part of teaching Sections 6.5 and 6.6, I heavily emphasize free energy diagrams (see, for example, Figures 6-6, 6-7, and 6-8). By associating the lower pKa with the more downhill or less uphill deprotonation, students gain a much better feel for the role that charge stability plays in acid strengths. Thus, these free energy diagrams become a powerful tool for students to use when they need to predict relative acid strengths on the basis of molecular structure. Students first write out the complete deprotonation reactions involving each acid. Then students locate the vertical position of each set of reactants on the basis charge stability, and do the same for each set of products. Finally, students add curves to connect each set of reactants to the corresponding products, after which students can simply “read off” the relative acid strengths by noting the order of the curves from least downhill or most uphill (weakest acid) to least uphill or most downhill (strongest acid).
The benefits of using free energy diagrams as a tool for predicting relative acid strengths is most apparent when students need to predict the order of numerous acids at once. Section 6.7 (Strategies for Success: Ranking Acid and Base Strengths—The Relative Importance of Effects on Charge) brings students through an example of ranking four acids, culminating in the free energy diagram in Figure 6-14.
I don’t spend a lot of class time on Section 6.8 (Strategies for Success: Determining Relative Contributions by Resonance Structures), but I do make sure to cover the basics and present at least one example. The material in this section is essentially just an application of charge stability toward a concept that students learned in Chapter 1: the lowest energy resonance structure has the greatest contribution to the hybrid. Thus, I principally use Section 6.8 as a means by which to reinforce what students just learned in Chapter 6 pertaining to predicting the relative stability of charged species.
Chapter 7 (An Overview of the Most Common Elementary Steps) is a vital part of getting students to succeed with mechanisms throughout the entire course. The chapter brings students through the ten most common elementary steps that will constitute all of the mechanisms that appear in the book through Chapter 23. This alone is a very powerful message for students: The many hundreds of reactions you will see are built from just these few elementary steps. The idea is to motivate students from the very outset that studying mechanisms is worth the investment because mechanisms allow us to see patterns emerge that we otherwise couldn’t see; mechanisms simplify organic chemistry.
Beyond motivating students to value mechanisms, Chapter 7 gives students the tools to comfortably work with mechanisms by dissecting key aspects of the ten elementary steps. For each elementary step, students are taught (1) the major players that act as reactants and products, (2) the curved arrow notation that describes the bonds breaking and forming, and (3) how that curved arrow notation demonstrates the flow of electrons from an electron-rich site to an electron-poor one. Thus, students can begin to propose reasonable elementary steps given only a set of reacting species. For example, if the reacting species are the ethoxide anion and acetaldehyde, a student can very quickly see the ethoxide anion as a nucleophile and acetaldehyde as having a polar bond—major players involved as reacting species in a nucleophilic addition step. Immediately, the student would know to draw one curved arrow from the electron-rich O of the ethoxide anion to the electron-poor C of the carbonyl group, and to draw a second curved arrow from the center of the C=O bond to the connected O. Finally, the student can follow the curved arrow notation to arrive at the product. Alternatively, a student who recalls the pKa values they learned in Chapter 6 can see those same two reacting species as a base and an acid—major players involved in a proton transfer step—and can draw the appropriate curved arrow notation to arrive at the products.
Having these tools to work with elementary steps, I find it valuable at this point to expose students to multistep mechanisms in a somewhat low-stakes fashion, using the Integrated Problems at the end of the chapter. Problems 7.46 through 7.55 provide complete mechanisms of reactions students will encounter later in the book, and ask students to add curved arrow notation, identify electron-rich and electron-poor sites, and name the elementary step. Problems 7.56 through 7.60 give students an initial set of reactants and a sequence of elementary steps by name, and ask students to apply the appropriate curved arrow notation to arrive at the product of each elementary step. These Integrated Problems facilitate students becoming more intimate with the details of each type of elementary step. Additionally, they help remove the intimidation that students might otherwise face with multistep mechanisms down the road. When higher expectations pertaining to reactions are placed upon students—such as stereochemistry, regiochemistry, and predicting products—students can rest a bit easier having already had experience working with multistep mechanisms.
In addition to familiarizing students with key aspects of the ten common elementary steps, Chapter 7 gives students two other very helpful tools. Section 7.1b (Simplifying Assumptions Regarding Electron-Rich and Electron-Poor Species) teaches students how to simplify species when drawing mechanisms, such as treating LiAlH4 as a source of Hˉ and Grignard reagents as sources of Rˉ. As students are first starting out with mechanisms, it helps to keep complications to a minimum. Section 7.8 (The Driving Force for Chemical Reactions) teaches students how to use charge stability and bond energies (in that order of importance) to determine whether a proposed elementary step is favorable. Down the road, this will help students predict whether it is reasonable for an elementary step to occur at a certain point in a multistep mechanism, and whether that step is reversible or irreversible.
Chapter 7 is a vital chapter, indeed, but it is also important to avoid overwhelming students with excessive details that can be associated with each elementary step. Take, for example, the SN2 step. As instructors, we know there is a lot that could be said about SN2 reactions, such as: the inversion of stereochemical configuration; the fact that the reaction cannot occur with tertiary substrates; its bimolecular kinetics; and the competition with SN1, E2 and E1 reactions. These are all details that will be covered in due time—Chapters 8 and 9 in this case—so I would strongly recommend avoiding the temptation of teaching aspects of the reaction that do not appear in Chapter 7. As far as Chapter 7 is concerned, I like to say: “Check your baggage at the door.” For me, the proper balance is to spend about two class periods on the Chapter.
In other organic chemistry textbooks, some combination of SN1, SN2, E1 and E2 mechanisms are introduced in the same chapter that also deals with predicting the outcome of the competition involving those reactions. In my textbook, dealing with the competition among these reactions is separated from the material that deals with aspects of their mechanisms. The SN2 and E2 mechanisms are presented as elementary steps in Chapter 7, and the SN1 and E1 mechanisms are introduced in Chapter 8. Then, Chapter 9 is devoted entirely to the competition among the SN1, SN2, E1 and E2 reactions. The main thrust for organizing the material this way is to combat memorization and to reinforce the value of mechanisms.
Students by and large enter organic chemistry convinced that the most important aspect of the course is predicting products of reactions and, furthermore, that the reactions must be committed to memory in order to predict products. For these students, it can be detrimental to deal with the SN1/SN2/E1/E2 competition in the same chapter the mechanisms are introduced because of how strong the pull is toward predicting products; it plays into the hands of students’ misconceptions. By contrast, with the SN1/SN2/E1/E2 competition limited to Chapter 9 only, aspects of the mechanisms for these reactions take center stage in Chapters 7 and 8. Thus, students come away from Chapters 7 and 8 with a greater value of the insights that mechanisms offer toward understanding reactions, and that mechanisms are worthwhile. This sets an important precedent for learning reactions throughout the rest of the book.
Another important reason for organizing the SN1/SN2/E1/E2 material this way comes from the ability to bring some key tools for working with multistep mechanisms to the forefront. In Chapter 8, students are taught how the stereochemistry and kinetics of reactions are rationalized from the mechanism. Furthermore, Chapter 8 introduces very useful rules of thumb for multistep mechanisms, such as how to reasonably incorporate proton transfers and carbocation rearrangements into multistep mechanisms. These concepts, if presented alongside predicting the major products of the SN1/SN2/E1/E2 competition, often become buried and tend to be overlooked by students.
Finally, dedicating chapter 9 to the SN1/SN2/E1/E2 competition more effectively promotes the process students are taught to predict the outcome. The process that students are taught asks students to consider the various factors that control the reactions rates: type of substrate, nucleophile/base strength and concentration, leaving group ability, solvent, and heat. If instead the mechanisms of the reactions—and various aspects such as stereochemistry and kinetics—are introduced in the same chapter that such a process is also presented, students too often become overwhelmed. Rather than commit to learning and applying that process, students tend to look for shortcuts to memorize.
To recap, I have devoted Chapter 9 entirely to the competition among the SN1/SN2/E1/E2 competition to promote learning and understanding, and to deter students from memorizing. Students can focus on aspects of the mechanisms in Chapters 7 and 8 before being accountable for predicting the major products of the competition in Chapter 9.
Section 9.12 (Kinetic Control, Thermodynamic Control, and Reversibility) is located toward the end of Chapter 9, and you might be tempted to skip it or gloss over it. The material in that section is important, however, because it helps students build proper tools for predicting the major products of competing reactions—one of the most challenging tasks students face in organic chemistry. Students first face this challenge in Chapter 9 when they must determine the predominant mechanism in the SN1/SN2/E1/E2 competition, but they must also face this task with other competing reactions throughout the book, such as: competing elimination reactions (Zaitsev’s rule), competing reactions involving electrophilic addition steps (Markovnikov’s rule and o/p- vs. m-directors), competing deprotonations at carbons (kinetic vs. thermodynamic enolates), and nucleophilic addition to a carbonyl group competing with conjugate addition or enolate formation. Because students are routinely tasked with these kinds of competitions, I make sure to give significant emphasis to Section 9.12 in class, and I strongly recommend that you do as well.
One of the most important concepts from Section 9.12 to get across to students is that the outcome of a competing set of reactions can differ depending on whether the competition takes place under kinetic control or thermodynamic control. Students must therefore know whether they should try to determine the outcome on the basis of reaction rates or product stabilities. Without knowing that these two types of control exist for competing reactions, students have a tendency to limit their considerations only toward reaction rates.
Students are then taught how reversibility is linked to the type of control under which a competition takes place: a reversible competition effectively equilibrates the products, so the major product is the one that is most stable; in an irreversible competition, the products, once formed, are there to stay, so the one that accumulates the fastest is the major product. In short, a reversible competition tends to take place under thermodynamic control, whereas an irreversible competition tends to take place under kinetic control.
Finally, a critical piece to implementing this tool for predicting the outcome of a competition is to determine whether the competition takes place reversibly or irreversibly. Students are shown that this depends principally on how energetically stable the products are relative to the reactants, and the free energy diagram is a very helpful visual aid to get this point across.
Students will be far more successful predicting the products of competing reactions when they can reliably determine whether the competition is reversible or irreversible, and then apply that knowledge toward establishing kinetic or thermodynamic control. Training students to evaluate free energy diagrams to establish reversibility goas a long way toward helping students along these lines. Conversely, students who are not proficient doing these kinds of things tend to rely predominantly on memorization, a tactic that we know is destructive.
The biggest reason I wrote this textbook was to facilitate students learning and understanding the material rather than memorizing it. Organizing the reactions according to mechanism goes a long way toward reaching that goal, because students can see patterns emerge they otherwise wouldn’t see. In a similar vein, it also helps quite a bit to remove distractions from the early reaction chapters, when students are first learning reactions and mechanisms. That is why, for example, nomenclature and physical properties are dealt with elsewhere, giving students more time to focus on each topic at hand. It is also why I placed the first chapter on synthesis strategies, Chapter 13, where it is. By that point, students will have been through four chapters dealing with mechanisms and predicting products of reactions—Chapters 9-12—so a student’s foundation working with mechanisms will be solid before shifting gears in a big way to deal with synthesis strategies.
I feel that it is very important for students to have such a solid foundation working with mechanisms before dealing with synthesis strategies because of the danger that synthesis has in promoting memorization. Students by and large enter the course already convinced that they must commit a large number of reactions to memory, and asking students too early to develop quick recall of reactions that carry out specific changes to a molecule—a must for organic synthesis—can have the effect of devaluing mechanisms. Why should students spend time studying mechanisms if they believe their primary goal is to excel at synthesis? The location of Chapter 13 for synthesis strategies strikes a good balance: It comes after students have spent four chapters developing buy-in for mechanisms, so there is little risk of students ignoring mechanisms down the road, but it’s still early enough that students don’t lose sight of how the reactions they’ve learned can be applied.
That being said, some instructors will want students to work with significant aspects of synthesis prior to Chapter 13. One way to do so is to assign the end-of-chapter problems denoted “SYN,” which begin in Chapter 9. Prior to Chapter 13, these SYN problems have students deal with relatively simple, low-level aspects of synthesis—things students can deal with comfortably without specifically having learned some of the strategies presented in Chapter 13. Students might be asked for the reactant or the reactions conditions necessary to carry out a one-step synthesis. These kinds of problems help develop the mindset for more complex aspects of synthesis students will soon face.
Perhaps you want to take this a bit further, having students deal with multistep synthesis prior to Chapter 13. If so, you should feel comfortable teaching parts of Chapter 13 earlier. However, I would recommend not moving the material earlier than immediately after Chapter 10. Otherwise, you would run the risk of undermining the value of learning mechanisms, and you would also run the risk of students not having learned reactions that are suitable to demonstrate a particular synthesis strategy.
If you do decide to teach some of the Chapter 13 strategies earlier, be sure that the examples showing how to apply the strategies incorporate only the reactions that have been taught. For example, consider the following if you decide to move some strategies from Chapter 13 to immediately after Chapter 10:
Section 13.1. Writing the Reactions of an Organic Synthesis
o Avoid Equations 13-4, 13-5, 13-9
Section 13.4b. Synthetic Traps and Regiochemistry
o Avoid Equations 13-19, 13-20, 13-21, 13-22, 13-23, 13-24, 13-29, 13-
Section 13.5. Choice of the Solvent
o Avoid Equations 13-31, 13-32, 13-33
Section 13.6. Considerations of Stereochemistry in Synthesis
o Avoid Equations 13-44, 13-45, 13-46, 13-47, 13-48, 13-49
Section 13.7. Strategies for Success: Improving Your Proficiency with Solving Multistep Syntheses
o The example given incorporates the addition of Br2 across a C=C
double bond, so you will need to construct an example that
incorporates only reactions from Chapters 9 and 10.
Section 13.8b. Green Chemistry
o Avoid Equations 13-50, 13-51, 13-53, 13-54, 13-55
Students often have to shift gears in significant ways when they begin to learn organic synthesis. Rather than focusing on the incremental changes brought about by elementary steps, students must focus on the big differences between the overall reactants and products. Rather than think in the forward direction, students must think retrosynthetically. And students are often called upon to work through trial and error, due to the open-endedness of synthesis design. To help students navigate this shifting of gears, I have included some key features in my textbook.
One really helpful feature is the collection of all the reactions in the book in Appendices C and D. Appendix C is a single table that contains all the reactions that alter the carbon skeleton. Appendix D contains all the functional group transformations, organized into tables according to the compound class that is produced. Organizing the reaction in the appendices like this is immensely useful when students are just beginning to learn retrosynthesis. When a student tackles a synthesis problem, they initially focus on the target and ask questions like “what reaction will produce an alcohol?” or “what reaction will produce an amide?” or “what reaction will form a C-C bond involving an C?” By answering these questions, students have candidates they can implement in their synthesis design, and arrive at precursors. Students then shift their focus to those precursors and ask similar questions. And with the tables organized the way they are in Appendices C and D, students can quickly find the answers to these kinds of questions. To answer the first question, for example, students would turn to Table 3 in Appendix D. To answer the second question, students would turn to Table 9 in Appendix D. And to answer the third question, students would turn to Appendix C.
Having students use Appendices C and D like this is really helpful, first of all, because it minimizes frustration when students are looking for the right reaction to carry out a specific task. Retrosynthetic analysis is immediately awkward for many students because of the requirements to think in the reverse direction. Any substantial frustration added on top can be the tipping point for students to abandon retrosynthetic analysis altogether. Second, using Appendices C and D like this can help students prioritize how they spend time studying. Each time a student goes to one of these appendices to find a reaction to carry out a specific task, it’s a message that (1) the reaction is useful, and (2) the student had difficulty recalling it when it mattered. Thus, the reactions for which a student uses Appendices C and D the most are the reactions that students ought to study the most.
Another really helpful feature of the book I use to help students master synthesis is Section 13.7, Strategies for Success: Improving Your Proficiency with Solving Multistep Syntheses. This section teaches students to design their own synthesis problems and then trade with a study partner to solve those syntheses. Of course solving those syntheses gives students additional practice applying the principles of retrosynthetic analysis and finding the appropriate reactions to carry out the necessary transformations. But in addition, a very helpful part of this exercise is students designing their own syntheses. To do so, a student must begin with a functional group embedded within a carbon structure of the student’s choosing, assigning that molecule as their starting material. Then the student decides what transformations to carry out, keeping track of the necessary reaction for each transformation. After a handful of transformations, the student’s final product becomes the target of the synthesis. This exercise designing a synthesis is quite helpful because, to choose each transformation, a student must ask questions like “What reaction can I carry out on an alkene?” or “What reaction can I carry out on a nitrile?” These kinds of questions test a students’ familiarity with the reactions that a functional group can undergo. If a student struggles to come up with more than two or three answers, then two things should happen. (1) The student should be directed to Appendix B: Characteristic Reactivities of Particular Compound Classes. There, students can find the functional group of interest and quickly see what kinds of transformations can be carried out on it. References are provided to the specific sections where each transformation is discussed. Similar to what I described above, this helps to avoid student frustration, which prevents students from abandoning this important exercise. (2) Also, similar to what I described above, each time a student turns to Appendix B to come up with various transformations to carry out, the student should keep note of it as guidance for which reactions deserve more of their attention when studying.
Even though Appendices B, C, and D have been in the textbook since the first edition, I started incorporating them into the classroom directly just this year. My students were performing solidly with multistep synthesis problems before last year. But when I began to incorporate those appendices into the classroom, my students began to perform even better. I will continue to show students how to make use of these appendices in the years to come.