Editing Transition state (section)

== The Hammond–Leffler postulate ==

The [[Hammond–Leffler postulate]] states that the structure of the transition state more closely resembles either the products or the starting material, depending on which is higher in [[enthalpy]]. A transition state that resembles the reactants more than the products is said to be ''early'', while a transition state that resembles the products more than the reactants is said to be ''late''. Thus, the [[Hammond–Leffler Postulate]] predicts a late transition state for an [[Endothermic process|endothermic reaction]] and an early transition state for an [[Exothermic process|exothermic reaction]].

A dimensionless [[reaction coordinate]] that quantifies the lateness of a transition state can be used to test the validity of the [[Hammond–Leffler postulate]] for a particular reaction.<ref>{{cite journal|title=A dimensionless reaction coordinate for quantifying the lateness of transition states |journal= Journal of Computational Chemistry|year= 2009|doi=10.1002/jcc.21440|author1=Thomas A. Manz |author2=David S. Sholl |volume= 31|issue= 7|pages= 1528–1541|pmid= 19908292}}</ref>