transition state

Chemical bond is stable state with relatively low potential energy. See Figure 1. Collision, heat, or radiation can stretch, twist, or compress chemical bond to maximum extent {transition state}| {activated complex}, as molecule electrical attractions resist chemical-bond disruption. Transition state has greatest disruption, highest potential energy, and maximum separation. See Figure 2. If it can become new conformation or molecule, transition state is hybrid of stable chemical states before and after chemical reaction.

From transition state, molecules can go back to original states or become new conformations or molecules, with equal probability. See Figure 3.