Initially you’ll have no choice but to remember all the reactions. It won’t be very difficult if you read through the reactions 4–5 times, and will easily cruise through the questions. Oh and if you find some random thing happening in some reactions it’s mostly because of the fact that Organic Chemistry is a complete subject and cannot easily be classified into chapters as we usually see. So don’t worry you’ll find abut it sooner or later
And as you’ll proceed forward through organic chemistry(class 12 book 2) you’ll easily be able to find logic in a lot of stuff you crammed earlier and will be able to write the mechanisms for some reactions.
So depending on your current situation, use the above mentioned information to study efficiently.
All the Best 🙂