CH-005 - Isomers Cheat Sheet

Today I looked at my hands and I realized they are enanti­omers of each other and now I'm stuck in a nightmare world where I can't escape from these things.

This is probably not super useful, and I might be missing stuff. It's just a basic checklist for my sanity :S

1. Find all the structural isomers (lol enjoy T_T)

2. Check for any chiral carbons. If there are any, you need to find the S and R enanti­omers. There might be several chiral carbons per molecule, and if so, you'll need to find every permut­ation of S- and R- carbons!

3. Check for any double­-bonds. If there are any and you can assign priorities to the groups on each carbon, you need to find the E and Z isomers.

Isomers are DIFFERENT MOLECULES that share the same chemical formula.

In the order they were introd­uced:

1. Structural isomers
2. Enanti­omers (S/R)
3. E/Z (trans­/cis) isomers

Things can be '­str­uctural isomer­s', meaning they have the same chemical formula, but in a completely different structure.

(note: 2-meth­ylp­ropane is also known as iso-bu­tane! see the table to the left)

Enanti­omers are mirror­-images of each other.
This is the case when one of the carbon atoms is chiral, or when that carbon is bonded to 4 unique groups.

1. Assign '­pri­ori­tie­s' -- highest priority goes to the highest atomic number. If there are multiple atoms of the same atomic number, give higher priority to the group that has the most overall stuff in it.
2. Send the lowest priority atom to the back. This is usually hydrogen.
3. Count 1->­2->3, where #1 is the highest priority.
4. If counting 1->­2->3 takes you clockwise, then it's (R). If anti-c­loc­kwise, it's (S).

These only occur around a double­-bond. A hydroc­arbon with a double­-bond is known as an alkene.

1. Look at the 2 groups on each of the 2 carbons.
2. Assign priorities on each side.
3. If both carbons have their higher priorities on the same side, it's a cis or (Z) isomer. If they're on different sides, it's a trans or (E) isomer.