Energy barrier :
For the reacting species to make effetive collisions they should havesufficient energy to break the chemical bonds in the reacting molecules. The minimum amount of energy which the colliding moleccules must possess is known as threshold energy. This means that only thosecollisions of reactants which possess energies greater than thresholdenergy will give products.
In the case of conformational isomerism, the energy barrier which prevents one conformer to convert into another by rotation, is called as orientation barrier.
