Himanshu Rajput I assume your objective is to study a chemical reaction (molecular mechanism, reaction energy...) utilizing IRC calculations. the Intrinsic Reaction Coordinate IRC computation is used only to verify the nature of a transition state that has been already found. So you should firstly perform QST2 or QST3 calculations (or other methods) in order to find a fine Transition State TS structure (because the calculation will use it as starting point to follow the gradients toward reactants in one side and to products in the other side) and approve it by FREQ calculations and then do IRCs to search reaction pathways.

Himanshu Rajput Please refer to attached document about " - How to find a transition state for an electrophilic addition with Gaussian and map the reaction pathway?"