Transition state

![The DFT-determined geometry for the transition state of the above reaction.[2] Distances are listed in angstroms. Note the elongated C-Br and C-O bonds, and the trigonal bipyramidal structure.](/uploads/202502/17/Base_hydrolysis_of_bromoethane,_TS0021.png)

The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules always go on to form products. It is often marked with the double dagger ‡ symbol.