well iit jee has no fixed pattern, anything can be asked ! but you must do all the reactions given in jee syllabus for organic chemistry thoroughly with their mechanisms !! some of which includes :-
1 Wurtz reaction and decarboxylation reactions.
2 Electrophilic substitution reactions(benzene): halogenation, nitration, sulphonation, Friedel-Crafts alkylation and acylation
3 Reimer-Tieman reaction, Kolbe reaction.
4 Grignard reactions
6 Williamson’s Synthesis
7 aldehydes and ketones : oxime and hydrazone formation; aldol condensation, Perkin reaction; Cannizzaro reaction; haloform reaction and nucleophilic addition reactions (Grignard addition)
8 stefans reaction
9 Sandmeyer and related reactions of diazonium salts
* this is not the complete list. i have given only those which are highlighted in jee syllabus and hence are important.