first optimize the reactant and the product (after rotation)
then use SCAN or Modredundant to calculate the energy of each stationary point along the rotation (according to the specific molecule and calculation); find the stationary point with the highest energy.
last use TS (no freeze or limitation) to get the transition state based on the structure with top energy obtained from SCAN or Modredundant.
Freq and IRC confirmation is necessary.
In a word, such rotational transition state is difficult to obtain. Maybe u have to do a lot of tries.
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