How do reactants 'react' to become products?

Inorder for a reaction to occur the reactants, the BG molecule and R atom, must collide with the proper orientation. The R atom must collide with the G atom of the BG molecule.

Additionally, even when the orientation of the collision of the BG molecule and the R atom favors the products, if the collision does not have sufficient energy no reaction is observed.

Finally, the reaction occurs in a single step.