Organic chemistry. If you are pre-med, pre-dentistry, pre-pharmacy, a biology major, going into the health care or pharmaceutical industry, or any kind of science kid, you will, at some point, have to tackle this beast. You hear all the rumors, know all the people who’ve had to retake it for one reason or another. You sign up for the class (almost invariably scheduled for 8 or 9am, and you buy the model set. But you still aren’t really prepared.
Before taking O chem, I had a year of general bio, a year of anatomy & phys, several other bio classes (immunology, cell bio, molecular bio), and a year of gen chem. You would think that would be good preparation, and it was definitely better than not having that background, but O chem is a beast of a different nature. It is nothing like gen chem, which is full of chemical reactions and equations, measurements, masses, temperatures and (somewhat) straightforward physical laws. The first few days of O chem review some things from gen chem (oribital hybridization, VSEPR and molecular shapes), but from then on it is all new material, like nothing you have ever seen before. My prof always said that’s part of the point, to see how you handle something completely new.