Hammond postulate definition

The usual experimental approach3 is based on the Hammond postulate (Hammond, 1955). A transition state, which lies by definition between the starting materials and products for a particular step of a reaction, is supposed to be closer in structure, because closer in energy, to the higher energy species of the two. Various techniques, particularly linear free energy relationships, are available to compare the effects of various probes... 

The form of the Hammond postulate just presented is very important in the analysis of the selectivity of many of the reactions we will discuss in this book in connection with chemoselectivity (definition in Section 1.7.2 also see Section 3.2.2), stereoselectivity (definition in Section 3.2.2), diastereoselectivity (definition in Section 3.2.2), enantiose-lectivity (definition in Section 3.2.2), and regioselectivity (definition in Section 1.7.2). 

A general definition of the Quantum Molecular Similarity Measure is reported. Particular cases of this definition are discussed, drawing special attention to the new definition of Gravitational-like Quantum Molecular Similarity Measures. Applications to the study of fluoromethanes and chloro-methanes, the Carbonic Anhydrase enzyme, and the Hammond postulate are presented. Our calculations fully support the use of Quantum Molecular Similarity Measums as an efficient molecular engineering tool in order to predict physical properties, lMok>gical and pbarraacdogical activities, as well as to interpret complex chemical problems. 

In other words, under these restrictive conditions, outer sphere electron-transfer reactions obeying the Marcus-Hush model are typical examples where the Hammond-Leffler postulate and the reactivity-selectivity principle (see, for example, Pross, 1977, and references cited therein, for the definition of these notions) are expected to apply. 

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