Unfortunately, what you’re doing will not look good to adcomms.
The assumption for the P/F will be that you were not doing doing well in the class, that at best you would have earned a C, perhaps even a C- or D. (Why else would a pre-med take pre-req P/F?) Then you transfer to CC–which will be viewed a step down in competitiveness from your UC–and the picture is not one of student who challenges himself academically. And now you’ve put yourself in a bind because even if you do earn an A in your gen chem class at the CC, the impact of that A will be lessened because it’s your second time through the material and an A grade is expected.
I understand why you made your decision, but it probably wasn’t the best choice you could have made. (My older D transferred from a quarter system college to a semester system college and only got partial credit for her classes. However, she didn’t repeat coursework. Instead she petitioned the chem dept. to allow her to advance to the next level class–something that was readily granted. She did have to take some additional classes to make up for having 3 credits instead of 4 for some GEs required for graduation, but she took different classes and didn’t simply repeat ones she had already partial credit for.)
BTW, attending a private college doesn’t necessarily guarantee you smaller classes. Unless you attend a very small college with just a couple of thousand students, intro level classes (including OChem) are still going to be huge lectures with several hundred students.