A long but interesting letter from a reader who I’ll call “Annie” on how preparing for an exam the “right way” (learning the mechanisms for every reaction) as opposed to the ‘wrong way’ (flashcards) actually led to worse results (emphases are mine).
My entire life I’ve been hearing people say variations of “In first semester ochem you’re going to come to a fork in the road where some people will choose to memorize a whole bunch of stuff but other people will have no need to memorize because they will actually deep-down understand it. Make sure you’re in the second group because, man, [insert a zillion reasons].”
I took that to heart. I’m taking a compressed orgo course this fall; we just took our second exam last Friday, it was the first that had any mechanisms. Determined to not be one of these so-called memorizers, I spent the whole weekend learning maybe thirty mechanisms from the ground-up, going through them again and again until all the arrow pushing was natural and understandable and routine. Of course some of these (say…ozonolysis) were pretty involved and kind of a pain and every second I sat in my kitchen learning it probably cost me three or four seconds of overall life expectancy.
But I’ll get to the point, and spoiler alert, it involves whining.
The actual test was unexpected. A typical mechanism question was “ok, here’s a goofy alkene: What would the product be if we applied these SIX reagents to it in this order?” And then the six reagents would just be stacked top-to-bottom on top of the central arrow.
I didn’t know there were going to be questions like that, and I”m only mentioning this because I suddenly felt like I was at a sort of a weird disadvantage. The way I had learned mechanisms, each one of those exam problems was necessarily a fifty-step deathmarch taking fifteen minutes each to solve, check, and recheck.
But for everyone who had just memorized thirty quick flashcards with only starting molecule / reagents / product, then those questions were thirty-second plug-and-chug victory laps.
While this email probably looks like I am just venting about how I feel misled or duped or that my friends in the class took the easy way out, that’s really not it at all, because on the contrary, I feel like they were all very smart about it, and that I completely lost the plot, because sitting here now, my ability to walk stepwise through the many mysteries of hydroboration seems not only sort of useless, but it legitimately hurt me on that exam: that section took me an hour and would have been easy to flub a methyl here or there, while meanwhile the whole flashcard army was getting all the points, and an extra hour on the test, and an extra week spent running barefoot on the beach towards a test which I assume for them was at worst good and at best an unequivocal markovnikovian triumph of drawing tiny tiny lines.
What happened here?
Let’s break down what happened.
- The student was given advice that memorizing reactions and mechanisms would have dire consequences.
- In preparation, she spent a ton of time learning all the mechanisms in detail, and didn’t rote-memorize the pattern of products formed in each reaction.
- When she took the exam, she felt she was at a disadvantage relative to her “flashcard army” peers, because she never learned to quickly determine what the product of a given reaction was without going through its mechanism.
- She feels cheated because she feels she studied the “right way” – spending a great deal of time learning arrow-pushing mechanisms – but was penalized for it, in that In the future, she’ll likely adopt the “flashcard” strategy that did well for her peers.
Essentially, this is a complaint about what was tested on the exam. Had her instructor tested people on their knowledge of mechanisms, she would have aced it. But instead, the exam tested the products of reactions – and in this respect, she was at a disadvantage, even through preparing for an exam that tests in this manner would have required less time to study for.
Explaining why it takes more time requires adding a figure. Let me show you an example of the type of question Annie is referring to:
Here, we’re given a starting alkene, and then are asked to apply the results of 4 reactions to get a final product (which I’ve shown in grayscale – obviously you wouldn’t see this on the exam).
The “quick” way to answer these questions is to know the pattern of what bonds are formed and broken in each reaction. This is something that is easily drilled by making flashcards.
[For instance, 1) HBr, H2O2 and hν is addition of HBr to the alkene under free-radical conditions. This breaks the C-C pi bond, and forms C-H and C-Br in a way that Br adds to the least substituted carbon [anti-Markovnikov addition]. This produces a new alkyl halide, and step 2) is addition of an acetylide, which does an SN2 reaction, forming C-C and breaking C-Br. Step 3) is Lindlar partial hydrogenation of an alkyne, which breaks the alkyne C-C pi bond, forming two adjacent C-H bonds in a way to make a cis alkene – and finally, step 4) is dihydroxylation of an alkene with OsO4 to give a syn diol: break C-C pi, and form two adjacent C-OH bonds on the same face of the alkene].
Annie’s way, which is much slower, requires drawing out the mechanism for each reaction in order to obtain the final product. That certainly shows deeper knowledge of each reaction, but it’s extremely time consuming.
What Instructors Test For Ultimately Determines How Students Study
Had the instructor had instead tested on the mechanisms of various reactions, it could very well have been a member of the “flashcard army” who emailed me with their “I studied badly” story, resolving to tear up their flashcards and instead learning the arrow pushing for each reaction in detail for the next exam. But how often does that happen?
Recently I looked at a few dozen exams (midterms and finals) in first semester organic chemistry, focusing particularly on alkenes. I found 334 exam problems. Of those 334, here’s how they broke down.
Predict the products: 201
Draw reagents/intermediate: 49
Give starting material: 11
Provide mechanism: 50
Of those 334 questions, 261 (78%) were some variation of a reaction that could be easily studied with a standard flashcard design (blanks for SM, reagent, and product). Only 50 (15%) concerned a mechanism. Now take that with a lot of salt, because mechanism questions are usually worth more points, and this was a relatively small sample of exams, as well as being just one section out of many in organic chemistry… but you get the idea. Students use flashcards because many instructors test their students in a way that rewards this method.
“Shallow” Preparation Takes Less Time Than “Deep” Preparation. So Most Students Should Start There.
Hence, I tell most students that it’s smart to “start shallow, then then go deep”. By that, I mean, focus on answering the “what” questions before you get to answering “how” or “why”. My classic “what” question, which will go on my tombstone, is “What Bonds Form, What Bonds Break?”. [I covered Shallow vs. Deep in my last post on “Learning Reactions: A Checklist“]. The factual questions take less time to learn than the tough work of learning to apply concepts (a skill which often takes a lot of practice problems to sharpen).
There are exceptions – I’ve tutored some of Maitland Jones’ students at NYU, for instance, and they learn pretty quickly that flashcards are not nearly as helpful as working a lot of different problems. And there are many other instructors out there who love to make their students think (University of Michigan, George Mason U, and a lot of schools in New York State, to start). But these are not the majority.
One last word which I hope students like Annie will take to heart. The weakness of the flashcard army is that they start to think that learning the facts of reactions is all there is. While it’s absolutely necessary to learn the facts, it’s even more important not to stop there, because many final exams (including the standardized ACS exams) can be very conceptual. Start shallow… but then go deep.