WuToWu #29: Spring, Housing, and Arrow Pushing (Pt. 2)

Hi Jessica,

The weather forecast says that the temperatures should get into the 50s next week, and I’m looking forward to getting some marginally warmer weather before heading down south for Spring Tour. It hasn’t been 50 degrees in months!

Le Petit Prince was my favorite part of French 3H, but the board game project was not my favorite part. I had actually read the book in English a while back, and I’m pretty sure we have at least two copies at home somewhere, so you can read those, just in case you missed some nuances in the French version. Je dois utiliser le francais plus souvent quand je t’ecris.

The Glee Club life never ends; even though we had a concert this past Saturday, I have rehearsal 5 days a week to get ready for tour. The repetoire is fun though: a piece by PDQ Bach, a newly commissioned work, Lamentations by Thomas Tallis, Moon River from Breakfast at Tiffany’s, I’ll Make a Man Out of You from Mulan, and Danny Boy. (The last three are lite pieces)

As always around this time of year, midterms are in the classroom, and the air is filled with the sound of hundreds of freshman trying to figure out who they’re going to live with for the next 3 years. Once everyone has made things suitable awkward with their friends, the next challenge is to come up with a name for your blocking group. Some of our ideas included:

  1. The Block Panthers
  2. Professor Sirius Block
  3. The Block Sheep
  4. To Kill A Blockingbird
  5. Supermassive Block Hole
  6. President Block Obama
  7. League of Extraordinary Gentlemen
  8. Army of Respected Men

Eventually we settled on a Star Wars reference: It’s A Trap!, which is a bit of an inside joke. Our linking group chose to go with The Block Panthers. In a little over a week, I will know what house I’ll be living in (unfortunately, circumstances have dictated that I have a higher chance of living in the Quad than most). The view from Weeks bridge hasn’t changed much, but I’ll send you another photo in the next post to demonstrate the existence of seasons on the East Coast.

Finally, you may have noticed that the chemistry lesson in the previous post lacked arrows, even though the title had the words “arrow pushing” in it. This is because I thought I would teach you about arrow pushing, but realized that you need to have an understanding of skeletal diagrams before we got to arrow pushing. So today, we’ll cover actual arrow pushing!

Arrow pushing is a convention that allows you to keep track of electrons, and consequently charges, in the course of the reaction. Here’s a simple resonance structure example:

Source: masterorganicchemistry.com

Source: masterorganicchemistry.com

In the first instance, the Oxygen has a negative formal charge, which is calculated using the formula: # valence electrons in normal, elemental state – # unpaired electrons – # of bonds. So in this case, 6 – 6 – 1 = -1. The carbon atom has a positive formal charge, as 4 – 3 = 1.

You might be thinking to yourself, “hey, that carbon only has 6 electrons!” And you would be right. A carbon with an incomplete octet is fairly unstable. Therefore, two of the electrons on the oxygen atom will move to form a bond with the carbon (in molecular orbital talk, that would be a non-bonded oxygen to pi-bond interaction).

The final product has a neutral charge on both oxygen and carbon, which is the most stable state. This is an important idea in any chemistry class, so if you get one thing from this lesson, let it be this: Minimize Formal Charge. 6-4-2 = 0 for oxygen, and 4-0-4 = 0 for carbon.

Arrow pushing can help you keep track of electrons in more complicated reactions:

Source: walba.colorado.edu

Source: walba.colorado.edu

Disclaimer: don’t use any part of this mechanism in your chemistry class, because it pretty much breaks all the rules for the simplified chemstry we learn in high school. Just consider it a way to practice following the electrons around the reaction.

For some of our readers who have experience with organic chemistry, you might recognize this as a unimolecular beta-substitution reaction, or Sn1.

That’s all I have for you today!



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