How can I take effective notes during lectures on complex topics like quantum mechanics and organic chemistry without getting overwhelmed by the amount of new information?

Stop trying to capture everything the professor says in real time. When you focus on transcribing, your brain acts like a photocopier rather than a processor. Instead, treat the lecture as a live demonstration where your only goal is to identify the logical flow of the argument. Write down the core concepts and the connections between them, but leave plenty of blank space on your page. Use that extra space to jot down questions or points of confusion immediately as they arise. If the professor explains a reaction mechanism or a physical principle, don't worry about writing down every step. Just note the "why" behind the shift from one state to another. If you get lost, mark it with a big question mark and keep listening; don't stop the lecture to fix it right then. The real magic happens within twenty-four hours of the class. Take your notes and try to explain the material to an imaginary peer without looking at your textbook. If you stumble, that is where your actual learning gap lies. Go back to your lecture notes or the source material specifically to bridge that one gap. This method forces you to engage with the structure of the information rather than just the surface-level details.