Advanced mechanisms can be difficult because they involve multiple transition states and unobservable intermediates.
At the advanced level, simply knowing that "H2/Pd reduces alkenes" isn't enough. You need to know why it works, when it fails, and how to manipulate molecules in a 10-step synthesis without losing your protecting groups. advanced organic chemistry practice problems
If you have exhausted your textbook's end-of-chapter problems, here are the "Holy Grail" resources for advanced practice: Advanced mechanisms can be difficult because they involve
These reactions occur via a single, cyclic transition state without intermediates. when it fails