hi,

see if you are weak in basic then it would take a longer time to grasp the full syllabus. organic chemistry is the most hard parts of 12th chemistry and it needs a lot of revision and practice to master the mechanism of the reaction. however you need one  good tutor who would high light the main topics of each of the syllabus. for cbse students ncert books is highly recommended. apart from this you may look for Reactions, Rearrangements and Reagents by S.N. Sanyal, Solomons’ Organic Chemistry or himanshu pandey.