The stuff you need for OChem is pretty much the stuff from chemistry that you'll never forget.
If you learned these in general chem, it'd serve you well to review them:
- orbitals/electron configurations/quantum numbers
- entropy and enthalpy
- determining the number of molecules from the mass of a sample
Those are all very important if you want to understand how the reactions work. Chances are, they'll reteach those skills.
Here's the thing with ochem. There are two ways to get through it.
1) Learning how chemical/physical properties determine which reactions are possible (based on energy chances, hindrance, luck, etc) This requires critical thinking more than anything.
2) Rote memorization. If you memorize everything, you can probably pass with a good grade. You'll spend a lot of time doing it, and you'll really never be able to apply your knowledge without an understanding.
Again, reviewing chem isn't necessary, but it would help if you're really gung ho about it.