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Coin Flip Game to Teach NMR Coupling and J-Value Concepts

One of the most frustrating units for me to teach in my sophomore organic chemistry class is the coupling/j-value concept in the NMR chapter. Going through the tree diagrams, we can get to a place where we understand that 3 neighboring protons cause a quartet, but I’m not convinced they really understand why. It gets worse when we get to doublet of doublets. This really goes way over their head. So I delve deeper into the theory so it will become more clear, but the concept only becomes more muddy in their mind. So I go even deeper, really getting into the physics (a class many of them haven’t taken yet), and their eyes start to glaze over and I start to lose the class.

By the end of the unit, we all resign and the students end up ‘memorizing cases’ with little to no understanding of why. I hate ‘memorizing cases.’

So last week I had an epiphany on the drive to work. I was thinking about how to make the concept more clear. Given a proton with a chemical shift, the random up or down spin state of the neighboring proton influences the chemical shift of the observed proton and offsets the chemical shift by an equal value in the positive and negative direction. Total values… a binary up/down spin state… offset by equal amount. Coins!

Given a quarter with a ‘chemical shift’ value of $0.25, a flipped penny will either land heads up or tails (heads down). Say a heads up penny adds $0.01 to the total value, and a heads down penny subtracts $0.01 from the total value. Flipping the penny thousands of times and keeping a running tally of the occurrence of the total values will give a statistical 1:1 ratio of total value $0.24 or $0.26. Flipping two pennies thousands of times will give a statistical 1:2:1 ratio of total values $0.23, $0.25, or $0.27. The analogy is perfect! And if you flip a nickel instead of a penny, we can even draw an analogy to j-values!

I was really excited about my new teaching tool, and began thinking about how to implement it in the classroom. Do I just talk it through as a pure thought experiment? No, they’ll drone me out. I can bring in a penny for everyone and we can predict outcomes, flip, and discuss as a class. Then pair up and play again with two pennies and discuss. That would work, and be interactive. But the relationship to NMR may still be fuzzy. It’d be nice if they could run lots of simulations with lots of combinations of coins on their own time…

Now, I’ve been participating in Code Year by Codecademy since it started in January. It’s been awesome. The first module in Code Year was JavaScript, a language I didn’t know but had always wanted to learn. My dad taught me BASIC when I was a kid, and I taught myself html and CSS, but I never knew JavaScript. I’m still not an expert, but I can code my way around JavaScript fairly confidently now, thanks Codecademy and Code Year!

So, feeling cocky with my new JavaScript tools, I thought this would be an excellent playground for me to test my new coding ability. If you want the entire story about how I created the site, all the gory details are below the jump. Many of you will not care. But after working on it for a week straight, it’s finally ready to launch. Here’s the game. Feel free to play around and see what you think.

Play 5 times to earn a link to a page digging into the theory.

If you teach NMR, and if you want to use this in your class, feel free to! I haven’t tested this out with an actual class of students who have never seen coupling/j-value yet, so we’ll see how it lands when I launch it for real 🙂 Hopefully the days of not understanding coupling/j-value are over!

If you have any comments/suggestions/improvement, I’d love to hear them!

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By June 7, 2012 15 comments chem 2.0, chemical education