Isomer Flowchart

Introduction

This is not one of my standard summaries of a topic. Due to a host of typical academic excuses, I haven’t had a chance to write a summary and associated one page handout/cheat-sheet. So instead, here is an isomer flowchart showing how you can classify isomers. There are multiple versions, showing the evolution of this chart … and I’m sure it isn’t finished yet.

Complete Isomer Flowchart

This is the current version. It could be called the postgraduate isomer flowchart. As with any discussion of stereochemistry, the more I thought about it the more complicated it became. Conformations and atropisomers, compounds that are differentiated through restricted rotation around a single covalent bond are where things became messy. I’m sure there are many chemists out there that are going to disagree with what I’ve done. Luckily, I’m easy going and happy to make corrections if people can give me a valid argument.

One discussion that has already arisen is the idea that the vast majority of compounds ‘are’ chiral as they only possess the necessary symmetry elements to be considered achiral in very specific and fleeting conformations. Its a wonderful philosophical discussion but I, like most chemists, have chosen to ignore it. If a compound has an achiral conformation then it is considered achiral even if most of the time it is a non-superposable mirror image (of course, including atropisomers on this chart blows this argument out the water instantly … and I’ve gone cross-eyed).

Simplified Isomer Flowchart

As the discussion about suggests, conformations make the discussion of stereoisomers more challenging. So a simplified version of the chart exists that just lumps everything into stereoisomers. Probably the better chart for the first few years of undergraduate study.

The Pictorial Flowchart

Then I wondered if I could make a pretty version of the flowchart. One that showed a bunch of molecules being separated into the different categories. I probably failed at this point. The version below is draft X, it works at A3 size but fails at the more useful A4. It needs work to fit everything onto one page and still make it legible.

Bonus Features - making of a flowchart

In the style of a DVD or, as this is a written piece, Jasper Fforde, I’ve include the behind the scene making of section.

Students and colleagues keeping saying “I wish I could make an attractive chemistry slide” just before presenting a hideous text-heavy PowerPoint presentation. This is odd as (a) we’re chemists, and everything we do is visual; and (b) we all know when something looks wrong/off. Just think about adverts/billboards. It’s obvious which are good and which aren’t. If we can see it in objects around us then we can all produce something that doesn’t look too bad (yeah, we’re not all artists but this about the placement of boxes and molecules on a page, not painting the Sistine Chapel). I think the real problem is that we just don’t have time to make things look nice and frequently default to a standard template. Now, I’m not saying that everything on this website looks nice and that I know what I’m doing (it doesn’t & I don’t … the whole point of this is to experiment and learn what works and what doesn’t). And that is the key … each of these handouts is the latest in a long iteration of attempts (at some point I simply run out of time and upload them). Each one could be improved if I did just one more draft (and then another …).

For the isomer flowchart, there were three handwritten versions:

First working drafts

Working sketch

After that I opened the laptop, Affinity publisher for the original flowcharts and Apple’s Pages for the pictorial version (with all molecules drawn in ChemDraw). Use of Pages is not recommended for this kind of thing, its distribution tool behaves very weirdly, I just happened to be doing most of that version on an iPad so was limited.

Below is the first version of the flowchart - it has a different flow across the page.

ADD HERE FROM LAPTOP

Conclusion

The first drafts always look ugly. Given time and enough drafts, good looking slides/handouts are achievable.