Transition State

What is a transition state? 

A transition state is a structure that represents an energy maximum on passing from reactants to products. It is not a real molecule in that, it may have partially formed and broken bonds and, may have more atoms or groups around the central atom than allowed by valence bond rules (ex. A pentavalent carbon)

It cannot be isolated because it is an energy maximum and any change in its structure leads to a more stable arrangement. 

A transition state is often shown by putting it in square brackets with a double-dagger superscript.

Pay attention!!!! A transition state is not an intermediate