For producing the effective collisions the colliding molecules must have
 

A reaction cannot occur if the particles do not collide with the activation energy of the reaction. If the atoms collide with less energy, the atoms simply bounce away from each other. Only collisions with energy that is equal to or greater than the activation energy will create a reaction. Ultimately, chemical reactions involve the breaking of some bonds (which takes energy) and making new bonds (which releases energy). Activation energy is the key to breaking the initial bonds.

In any collision involving unsymmetrical atoms, the orientations of the atoms during collision determine whether a reaction occurs; without the proper orientations during the collision, the reaction will not occur at all.