I'm studying a mechanism of aromatic substitution of fluorine which proceeds via an intermediate.
I'm searching for transition state using relaxed surface scan, then I optimize the TS and perform IRC (intrinsic reaction coordinate) calculation to verify the products. The problem is that the intermediate (that I get from IRC) has nearly the same energy as TS (about 1 kcal/mol lower), which doesn't seem right.
I assume that the intermediate geometry is wrong because the IRC makes 2-3 steps towards it and stops, saying the minimum was reached. How can I verify that IRC gives correct results?