Hammond principle (Hammond postulate). Also contains definition of: Leffler's assumption. The hypothesis that, when a transition state leading to an. In this section you will learn how the Hammond postulate helps you understand the relationship between kinetics and thermodynamics in. Hammond's postulate (or alternatively the Hammond–Leffler postulate), is a hypothesis in physical organic chemistry which describes the geometric structure of the transition state in an organic chemical reaction.‎Interpreting the Postulate · ‎Structure of transition states · ‎Applying the postulate.


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Hammond’s Postulate in Organic Chemistry Reactions — Master Organic Chemistry

This postulate is broadly hammond postulate below: Polanyi-Hammond postulate The mutual conversion between two species that are adjacent to each other on the reaction coordinate requires merely a minor change in the molecular structure if they have approximately almost the same energy.

Consequences of the Polanyi-Hammond postulate for the practice What does this mean in practice? If after the transition state an energy-rich intermediate stage directly follows on the reaction coordinate, this intermediate stage has just some trivial structural differences to the transition state.

The free energy diagram is shown in Figure 1. The tertiary carbocation with more substituted i. This is because the substituents stabilize the positive charge on the carbocation hammond postulate positive inductive effect.

Hammond’s Postulate - Chemistry LibreTexts

The factors that stabilize a full positive charge can be operated to stabilize a partial positive charge. Hence, the transition state for hammond postulate formation of a tertiary carbocation is more stable than that of a primary carbocation.


An approximation with their structural similarity assumption can be made. This is called Hammond's postulate, which is hammond postulate for George.

Hammond’s Postulate | OChemPal

Hammond, who first stated and used it in organic reactions in So the structure of the transition state more closely resembles the carbocation than hammond postulate alkene.

If two states, for example, a transition state and an unstable intermediate, occur consecutively during a reaction process and have nearly the same energy content, their interconversion will involve only a small reorganization of the hammond postulate structures.

This is a two-step mechanism.

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  • The Hammond Postulate (Polanyi-Hammond Postulate)

The more stable the carbocation intermediate is, the faster the reaction will proceed, favoring the products. Stabilization of the carbocation hammond postulate lowers the activation energy. According to Hammond's postulate, the more stable diastereomer is formed faster.

In an E2 mechanism, a base takes a proton near the leaving group, forcing the electrons down to make a double bond, and forcing off the leaving group-all in one concerted step. The rate law hammond postulate on the first order concentration of two reactants, making it a 2nd order bimolecular elimination reaction.


Factors that affect the rate determining step hammond postulate stereochemistry, leaving groups, and base strength. The adjustment involves much breaking of the bond more easily broken, and a small amount of breaking of the bond which requires more energy.

Hammond postulate: kinetic vs thermodynamics

The Hammond postulate is the opposite of what Bunnett theorized. In the transition state of a bond breaking step it involves little breaking when the bond is easily broken and much breaking when it is difficult to break.

Hammond postulate focuses on reaction steps where one bond is made or broken, or the breaking of two or more bonds occur simultaneously. The E2 theory transition state concerns a process when bond formation or breaking are not simultaneous.