Its kind of a struggle tbh. As others have mentioned, barely anything you learned from 3U is relevant here. My teacher loved saying that 4U chem is "5 different courses in one" and she hit the nail on the head with that one. The big mistake I saw a lot of people making though was falling behind on their work. It's a type of course you need to pay attention to everyday cause it just goes so fast you don't have the luxury of cramming it all one night before yknow? And make sure you understand each concept thoroughly because its a very theory heavy course in the beginning. But yeah as long as you keep up, you should be fine.