Well, it really depends on the order the book their using for ochem goes. But you absolutely should know SN1, SN2, E1, and E2. Know both the mechanisms (easy), and under what conditions each happens (a little harder). Know the naming of everything up to the point of second semester. That probably includes most of the IUPAC naming in the course. Certainly naming and reactions of alkanes, alkenes, alkynes (easy), grignards (organometalic rxns in general),. They probably have even reached reactions of aromatic systems, EAS, NAS. Some schools start with spectroscopy early, mine didnt touch it until the last quarter. That would entail picking up on IR, NMR, and mass spec., all of which take some time to get proficient at. I'm sure they've done stereochemisty, which plays a role in almost all reactions anyway. Some schools may even have done some keytone/ether/carboxylic acid chem by that point. I'm sure there are more possible first semester topics...
The difficult part about your situation is that if your second semester is heavy in retrosynthetic problems (ie. Make this molecule.), you may need to know a good deal of the first semester reactions. This was the case at my school, we needed every reaction all year long because you never knew when a synthetic problem would require a handfull of very old reactions to accomplish the steps after the part that included the new reaction he actually wanted to test you over. You would probably be best served to talk to someone at your school who took the first semester this year, or get ahold of the professor. Maybe get a list togeather of things that will be absolutely needed then go over them over break.
Good luck with that second semester of ochem, i'm sure if you put in the time you'll be able to excel.
