I took a year of O chem in a 10 week summer session. It was tough. Class/lab was 9-5 with an hour break but no 4 hour lab on friday. Every day you have to do your pre-lab/post-lab writeups(cheating was expected by our lab professor. everyone had his solutions to the labs and he didn't care if you turned in his solutions verbatim. the lab quiz was the great equalizer). Every other thursday was a lab quiz and every monday a midterm.
That said, I would do it again. I didn't do amazing(got two B's) but I think I focused too much on learning mechanisms when all I really needed to do was learn the products. I also wasted a lot of time reading the book whereas most people just went off their lecture notes. I would go ape**** trying to take o chem seriously while taking other classes at the same time.