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Hammond’s Postulate

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    • Hammond’s postulate states that the transition state of a reaction resembles either the reactants or the products, to whichever it is closer in energy.

    In an exothermic reaction, the transition state is closer to the reactants than to the products in energy (Fig. 1). Therefore, according to Hammond’s postulate, in an exothermic reaction, the transition state resembles the reactants.

    In an endothermic reaction, the transition state is closer to the products than to the reactants in energy (Fig. 2). Therefore, according to Hammond’s postulate, in an endothermic reaction, the transition state resembles the products.