Classification of Isomers Given that this is a long post, here's a quick index. The concept of how molecules can be "related" Non-isomers versus isomers Constitutional isomers versus stereoisomers Enantiomers versus 'non-enantiomers' (a.k.a. diastereomers) Diastereomers are … [Read more...]
s-cis and s-trans
s-cis and s-trans. What does those terms mean? Recall cis and trans. The reason Aldrich Chemical Co. can sell 99% cis-2-butene and 99% trans-2-butene in separate bottles is because of restricted rotation about the C-C pi bond. Rotation would destroy the overlap of the adjacent p-orbitals, and … [Read more...]
Assigning R/S To Newman Projections (And Converting Newman To Line Diagrams)
This post was co-authored with Matt Pierce of Organic Chemistry Solutions. Ask Matt about scheduling an online tutoring session here. In two recent posts we discussed how to assign (R/S) to configurations of chiral carbons in a variety of situations, both simple and more complex. So far, all … [Read more...]
The Ups and Downs of Cyclohexanes
Drawing cyclohexane chair forms can be a tricky business. While it's often intuitive to pick out which groups are up and down when they're axial (i.e. pointing straight up or down), it's tougher for beginners to see that equatorial groups (the ones pointing "somewhat up" or "somewhat down") can be … [Read more...]
On Cats, Part 3: Newman Projections
Do you know where the saying "there's more than one way to skin a cat" comes from? Me neither. But I do know one thing: there is more than one way to draw cat conformations. Last time I introduced the Cat Line Diagram and showed how we can use it to depict these 3-dimensional creatures on a … [Read more...]
On Cats, Part 1: Conformations and Configurations
[NOTE: this has been amended to correct some confusion on my part on the difference between configurational and constitutional isocats. Thanks to Prof. Gary Weisman (UNH) for making me aware of the error] As I said earlier, I've given up writing about organic chemistry. If you're expecting to … [Read more...]
The Many, Many Ways of Drawing Butane
One of the skills you have to develop early in Org 1 is to learn the different conventions for drawing molecules. Let's use butane as an example. Butane is pretty boring molecule, frankly. It's four carbons in a row. Not much more to it than that. However, even a simple molecule like butane … [Read more...]