A multitude of students have approached me over the years feeling frustrated about Organic Chemistry. Often, they would begin by telling me how many copious hours they have spent studying for their exam, quiz, etc. From my experience, this is due to studying the wrong way.
Students' first inclination seems to be to memorize bond breakage and formation. While this may help somewhat during the first semester of Organic Chemistry, what happens when there are more than 500 reactions? Well, all things seem equally possible and probable for students.
The answer is in the mechanisms ... For example, a Friedel Crafts (F.C.) alkyl reaction with benzene, CH3-CH2-Cl and AlCl3 produces ethyl-benzene. Yet, treatment with CH3CH2CH2Cl and AlCl3 does NOT produce n-propyl-benzene but isopropyl benzene! Why? That is because that there was rearrangement clearly predicted from the mechanism, but is not apparent otherwise.
Professors care about students' understanding of molecular behavior in solution, not memorization of bond breakage or formation. The exam or quiz questions may seem drastically unrelated to their notes. The answers are there, and they largely lie within the mechanisms.