Well, I took BOTH semesters of Ochem in ONE summer! Each semester was a little over 4 weeks long. I had to study my butt off--as far as I can remember, there WAS no summer that year--all I did was go to class, study, work, sleep...repeat!
doing this has its advantages--I was able to concentrate only on ochem, so I learned the material really well. Also, in one summer I was able to jump ahead a full year in the chemistry sequence.
Disavantages: learning the material is more up to you. The Prof fell behind at one point, so he skipped Nitrogen chemistry completely--had to teach all that stuff to myself!
So if you can handle it, go ahead and do it. As long as you take the classes at the same school, Adcomms won't care (at least no one ever asked me about it in interviews). Good luck!