Trapped in SN1/SN2/E1/E2 Hell? Some Resources

by James

in Alkyl Halides, Organic Chem Study Tips, Organic Chemistry 1, Organic Reactions

It’s that time of year when everyone starts making jokes about the backside attack. Here’s a few resources to check out:

  1. An SN1/SN2/E1/E2 summary sheet from FreelanceTeach: PDF
  2. Practice problems (and solutions) from Prof. Bill Reusch: link (go to right hand side under “Functional Group Reactions”, start at #16)
  3. SUNY Stony Brook Random Exam Generator – go to Chem 321 Exam #2 (this focuses on SN1/Sn2/E1/E2 as well as on some conformational analysis).
  4. Video series on SN1/SN2/E1/E2 from FreelanceTeach on Youtube
  5. In a hurry? My Org 1 Summary Sheets package includes both a flowchart of the SN1/SN2/E1/E2 and also a summary sheet that covers all the most important concepts in each of these reactions. Plus you get 18 other awesome summary sheets. It’s like having an instant set of study notes for your course!

Good luck!

 

 

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{ 18 comments… read them below or add one }

azmanam October 29, 2010 at 9:25 pm

I teach it to my class like we’re prosecutors in court trying to build a case for either SN1, SN2, E1, or E2. How do we build the case? We examine the evidence.

What evidence do we get from the nucleophile? It’s a good nucleophile, like I-? That’s evidence for SN2. It’s a poor base, like I-? That’s evidence against E2.

What evidence do we get from the elctrophile? It’s a primary halide? That’s evidence for SN2/E2 and evidence against SN1/E1 (because the resulting carbocation in the SN1/E1 mechanism would be a primary carbocation and we won’t form primary, unstable carbocations).

What evidence do we get from the solvent? It’s a polar aprotic solvent? That increases the nucleophilicity of the already strong nucleophile. That’s evidence for SN2

Then put it all together – look at all the evidence as a whole. I’ve got lots of evidence against an SN1/E1, a couple of pieces of evidence pointing toward SN2, and some evidence against E2.

Sounds like we’re doing an SN2 reaction!

Problem is, sometimes the evidence points in a couple of different directions – so how do we sort out the conflicting evidence and put together a case for one reaction pathway over another? That’s why this unit is so difficult. Sometimes deciding what the evidence means is really really hard.

I actually think trying to flow chart this problem is a bad way to approach it. It makes students think this is all ‘rules based,’ when really its so much more nuanced than that. To say we can flow chart this unit makes students think they can apply a set of rules and if I do things the same way every time, I’ll get a nice, neat, one single right answer every time. It’s way more complicated and nuanced than that.

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Calvin October 26, 2011 at 8:46 am

Just curious, im taking ochem right now…
Is this site still active/maintained?

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james October 26, 2011 at 9:22 pm

hell yeah!

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Calvin October 27, 2011 at 12:40 am

do you do short private tutoring sessions? say if i had a few questions on a certain homework problems, and need verfication, would you be available within a certain timeframe to be able to provide aid and guidance?

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james October 28, 2011 at 8:24 pm

right now given my current schedule that is just not possible. I realize there’s a demand for this kind of service however.

James October 30, 2010 at 4:27 am

Good point re the “evidence-based” approach versus a “rules-based approach”.

In light of the fact that ochem is a premed requirement, another way to look at it might be as a “diagnosis”. What can we rule out, based on the evidence? What’s consistent? What’s inconsistent?

This thought process is pervasive in medicine. My dad’s a retired GP and he had to use this kind of thinking all the time.

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Cindy November 3, 2010 at 3:34 am

HI James!!! Thanks for checking in and seeing that things are better with me and organic chemistry I am enjoying it a lot more than the first time around. I like th exam generator. That’s pretty cool! I’ve realized that it’s a looot of practice and critical thinking skills. It’s not something that you can memorize instead really thing about what is the next next. Over all I like it more than I thought I would in organic chemistry II. Thank you!!! i will use some of the info that you have on your blog for midterm II. Thank you!

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James November 3, 2010 at 8:56 pm

You’re welcome! Glad I could be of help.

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effieboo December 11, 2010 at 9:23 pm

Thank you thank you thank you! I love the flow chart. My Org 1 Final exam is in two days, wish me luck! :) Thanks for the great resources.

ps I’m a McGillian too!

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Vin January 18, 2011 at 6:14 pm

Thanks for the comments, very helpful and easy to understand!

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Coury June 20, 2011 at 9:31 am

I just came across this blog and it has been very helpful. I am taking Org 1 and 2 this summer… quite a challenge. Very fast paced so it is crucial to stay on top of the material and practice as much as possible. This past week we began learning mechanisms and they are giving me a hard time. I understand them individually but do not know how to determine which one needs to be used in different situations.

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James June 20, 2011 at 5:17 pm

This is an extremely common problem – for instance, understanding when something like OH(-) acts as a base and when it acts as a nucleophile can be tricky at first. The more problems/reactions you see, the more you’ll get the hang of it.

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UTPAL October 25, 2011 at 2:41 pm

THANKS !

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subhakar bhavarji April 1, 2012 at 11:04 am

thanq very much it is very useful to teach students

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K.G July 27, 2012 at 10:36 am

Thanks mate.. Really helpful info

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mak October 12, 2012 at 5:55 pm

This is an absolute lifesaver. Thank you. I was having a really hard time understanding how to choose one over the other. The flow chart was especially useful.

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Kim December 2, 2012 at 3:48 pm

James,

Thank you so much. I was so confused with substitution and elimination reactions. I understand them more clearly now all thank to you. Again, thank you. I truly appreciate the time and effort that you put in to make the tutorials available for free. Please keep up your good work.

Best.

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Karin November 12, 2013 at 1:56 pm

The whole overview for SN1, SN2, E1 and E2 is very clear. The only think I miss, which would make this picture even more complete to my opinion, is the E1cB mechanism. In which in which first a deprotonation of a β-hydrogen occurs followed by the loss of a leaving group from the α-carbon.

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