By now you should have a pretty good idea of how molecules orient themselves in space in terms of geometry and connectivity. Often, however, there is more than one way a molecule with a certain molecular formula can orient itself. It is important to be able to distinguish different molecules, even if they appear at first to be identical.
There are two major topics you should know in terms of distinguishing similar molecules, which I’m sure you can guess based on the heading. Isomers have the same exact molecular formula but a different arrangement of molecules, often giving them different molecular properties. Chirality has to do with a different orientation around one central, or chiral, atom. This concept is a little tougher to grasp at first, but with practice it should become very familiar.
The first thing you’ll need to understand is isomerism. Make sure you understand the different kinds of isomers, specifically diastereomers and enantiomers. Chirality can be a bit trickier, especially when it comes to naming. Understand that a chiral center is an atom with four different substituents branching off of it. You’ll need to know how to name a molecule using the R/S System of naming. This should become second nature with enough practice.
When naming a molecule using R/S, make sure the lowest priority atom/ substituent is in the back, facing away from the viewer. You can still name the molecule if the atom is in front as long as you remember to use the opposite name (i.e. use S instead of R or vice versa).
