Hammond’s Postulate

• The transition state of a reaction will resemble the reactants in an exothermic reaction.
• The transition state of a reaction will resemble the products in an endothermic reaction.

Perhaps it is not part of Hammond’s Postulate, but we also note that:

• For an exothermic reaction, the energy of the products is lower than the energy of the reactants.
• For an endothermic reaction, the energy of the products is higher than the energy of the reactants.