A reaction is most likely to occur when the colliding particles have proper orientation and energy.
Reactions occur when two reactant molecules effectively collide, each having minimum energy and correct orientation. According to the collision theory of reactivity, reactions occur when reactant molecules "effectively collide. For an effective collision to occur, the reactant molecules must be oriented in space correctly to facilitate the breaking and forming of bonds and the rearrangement of atoms that result in the formation of product molecules.