As a teacher, I occasionally experience situations that make me wonder if I am the worst teacher ever. There are times when, despite what seem to be my best effort, the point I am trying to make never sinks in. Sometimes after a bit of contemplation, I can figure out what went wrong and do something to correct the situation. But, occasionally there seems to be no solution. It is even more frustrating when the topic is fairly simple.
I recently had one of these frustrating episodes. In my Organic Chemistry class we have been covering substitution and elimination.
***disclaimer: To any non-chemists out there, much of this may not make sense. I'm not going to try to explain what I'm talking about, because based on the response of my students, I'd fail miserably.***
I put the following reactions on the board:
Many of you will recognize this as a classic question posed to organic chemistry students since Alexander first described his ether synthesis. One route will work quite nicely as written, but the other route is fraught with failure. Do you know which is which? If you've read this far, I'm sure you do.
Route A will work. Route B, however, will fail to make the desired product because elimination (to form 2-methylpropene) will predominate.
I put both reactions on the board and asked my students which one will work and which one won't.
I rephrase the questions to something like, "one of these is a valid strategy and one is not. Which one will work and which one will fail to make the ether?"
More dead silence.
I start asking leading questions, but nothing is clicking. I finally get annoyed and ask, "how many carbons do you need to form a double bond?"
A student timidly answers, "2?" I say, "exactly. Which reaction will undergo successful substitution?"
It went on like this for about 15 minutes. I could not get them to realize that in route A, elimination is impossible. Or, if they did, they could not explain it to me.
This has really annoyed me, because if the entire class fails to figure something out, the most likely culprit is me. Besides, the example I describe above is NOT a difficult concept. I spent about half of a class period describing the difference between the two.
I'll find our tomorrow if it worked. This is the first question on tomorrow's exam.
UPDATE: Only 20% of my students got the answer correct. The others chose B. This is preposterageous!!! They will learn.