Guest post by: Rami Ibo
On the occasion of the 2011 International Year of Chemistry, the Physical and Biophysical Chemistry Division (I) of IUPAC announced a Student Chemistry Cartoon Competition. The goal of the competition was to illustrate a chemistry principle in a manner that can enrich the teaching of chemistry (http://www.chemistry2011.org/participate/activities/show?id=361). So I decided to participate in this event and I drew by hand a chemistry cartoon which I called: SN2 vs SN1 rxns – Stories of Eternal Love & Conflict. 🙂
I sent in the cartoon along with the description that they asked for. Unfortunately, I did not win 🙁 (tears in my eyes and tissue box next to me :P)… However, I would still like to share it with you here on Sandpaw since I think the idea of teaching chemistry (or any science for that matter) in an accessible/humorous way is relevant to the discipline of Science Communication.
Here is the description of the cartoon. I hope you find it as informative and enjoyable as I did!
How does the cartoon relate to a chemistry principle?
It teaches in a simple and humorous way, the difference between SN2 (Substitution, Nucleophilic, Bimolecular) and SN1 (Substitution, Nucleophlic, Unimolecular) reactions in organic chemistry. I hope students will be able to relate to the cartoon and be able to notice the key features that distinguish between an SN2 reaction and an SN1 reaction.
Summary of the cartoon:
The cartoon is drawn on an A4 page and is split into two halves: the first half deals with SN2 reaction while the second half deals with the SN1 reaction. In the SN2 story, I introduce the main character of that story: CH3Cl in which the carbon is annoyed by the electronegative chlorine and how it withdraws all the electron density towards it [the chlorine]. Then I introduced the second character, OH–, which comes into the scene lonely and floating by. As soon as the carbon in CH3Cl and OH– see one another, they fall in love (much to chlorine’s dislike). As the bond between the OH– and the carbon forms, the bond between the carbon and chlorine starts to break (which is the key feature of SN2 reactions – it is a concerted mechanism where bond making and bond breaking happens at the same time). Chlorine leaves the molecule and becomes a chloride ion (which happens to be a very good leaving group as it can easily accommodate the extra negative charge).
In the SN1 story, OH–‘s twin brother (who unsurprisingly happens to be another OH– ion) meets CH3Cl’s older sister CR3Cl. Again, the OH– and the carbon in CR3Cl fall in love. However, it is not possible to form a bond between the OH– and the carbon of CR3Cl due to the bulkiness of the R (alkyl) groups (in other words, steric hindrance about the carbon prevents and SN2 reaction from taking place). This makes the couple sad. But in no time, the carbon in CR3Cl gets an idea! It figures out that in order to bond with OH–, it would need to break a bond first to create a vacancy (an SN1 reaction!). And in a very menacing move, the carbon “kicks out” the much disliked chlorine (in the form of a good leaving) from the molecule and becomes [the carbon] formally positively charged (a carbocation). And now, the OH– and the carbocation are able to form a bond and live happily ever after!
Note: For those who would like to use the cartoon, feel free to do so but please credit my name. Thank you.