Learning o-chem, flashcards v reaction mechanisms

This is a topic I am picking up from here. Coastie17 asked for helping in finding the best method to learn organic chemistry. You can find I had made two earlier posts in this thread.

Honclbrif: You should not have to work out the mechanism for every problem on an O-chem test. You’ll waste all your time on the first half dozen problems and leave everything else blank.

There is a grain of truth to this suggestion, but I don’t find that it applies to the poster’s question. I did not ask students to write out complete mechanisms for all of the problems for exactly the reason stated. It would take too much time even for me. However, I do mentally run through a mechanism if I cannot recognize how a product should form from the reactants. If a product is given and I cannot connect it mentally, then I too actually write out the steps to discover whether I might be making an error.

I told my class, “You don’t need to know every mechanism, only those that you want to answer on an exam.” A reaction mechanism is the organic chemist’s tools that he brings to a problem.

Honclbrif: The flash card method allows a student to rapidly answer certain questions about reactions…

This forum frequently clashes with posters. It asks that posters contribute to their learning (Rule #4). However, I fail to grasp how that is possible if a student is learning via flashcards. What is the point? Should I could tell a student which card to refer to?

There was a recent post asking for the product of an acid chloride and an amine (http://www.chemicalforums.com/index.php?topic=51617.0). We could take a cynical approach and castigate this student for not learning anything in their class, however I argue that we should arrive at a point in which we may find that there are many students asking this or similar questions. In fact, I believe the original poster was asking EXACTLY this. How do you memorize all of the reactions? This question is so elementary that I have to believe, either the student was not being presented with any mechanisms or the student was not grasping how reactions actually take place. (As in, “Had this student never seen nucleophiles add to a carbonyl group?”) From my own experience, I argue it is the latter. You can learn the products of a reaction without knowing how they take place (see examples here or here).

Mechanisms

I have discovered that even if you were to give a reaction mechanism to a student, tell them this exact problem will be on an exam, and test them with this mechanism, a number of students will be unable to write the mechanism. I have watched students struggle with writing reaction mechanisms. Even if clues are present that enable most students to add the curved arrows, many still struggle with them. I would argue this reality results in a compromise on the part of educators to devolve to flashcards in lieu of reaction mechanisms. I overheard a professor say, “You know, some students just don’t get mechanisms.”

Honclbrif: (Flashcards) … allows them to do the classic “what’s the missing reagent/reactant/product” questions (which I think are BS anyway, but what can you do?) which frequently can’t be solved by a mechanism.

Let me give my opinion on this statement. I don’t think one should expect a student to predict the reagents for a problem unless they can predict the products if given the reagents. I stand by that. Now, let me digress. There are some single step reactions in which no intermediates are drawn to help guide one in product formation. The only variation for a reaction of that type is to ask for the starting materials. Therefore, you will see that for Diels-Alder reactions, a problem will ask for the starting materials. In my book, in Part A, I ask for the curved arrows to be supplied. In Part B, I ask for the curved arrows and the product. In Part C, I don’t want to simply repeat Part B, so I ask for the starting materials to give the products. Let’s review. In Part B, I already asked for the product. If you can draw the product, only then should you be able to draw the starting materials. So, in instances like this, this seems a fair question, especially as it is the exact same question.

I don’t strictly avoid asking for starting materials or reagents. I simply view these types of questions as iterations of drawing the products. I like to practice a lot of drawing products before I ask for reactants.

Honclbrif: I’m not saying that students should not learn mechanisms. In fact, I emphatically say that they should. However, you can’t throw the baby out with the bathwater on this one.

I cannot discern if this is hyperbole. You should learn mechanisms, but you don’t really need to? You can learn just as well with flashcards?

I argue the opposite. You should learn reaction mechanisms. Reaction mechanisms teach chemistry. You learn how chemicals react from well written mechanisms. They teach you about chemical reactivity and alternate reaction paths. All of these rationalization should align with the laws of chemistry and physics.

I also concede that if someone learns a great number of reactions, they will remember the products or to be able to predict the products without writing out each step of a mechanism. Not only that, but as there are reactions in which the mechanisms are not known, that based upon other reactions, reasonable expectations, and rote memory, I have learned to predict the products as if by flashcard, that is, without any mechanistic theory.

I argue that by learning reaction mechanisms, you are learning the laws of chemistry and physics. By doing so, you will begin to find repetition because the laws are constant. They don’t change. Because patterns repeat, it becomes easier to learn another reaction. If you know French, it is easier to learn Italian.

*Note, while I have repeated Honclbrif’s quotations, I do not mean to single out Honclbrif. The arguments are quite universal. Honclbrif is not the only person to advocate flashcards. The examples I cited earlier (here or here) are academic sites showing flashcards. I presume these university’s are not abandoning reaction mechanisms, but they do advocate using flashcards. I strongly suspect the faculties also are thinking, “You know, some students just don’t get mechanisms.” They are fulfilling the adage, “If you don’t understand, memorize.” I simply think this is not good pedagogy.

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