And the Hammond postulate

Obtain the energies of propene, dimethylborane, and 1-propyldimethyl borane, and calculate AH n for dimethylborane addition. Is this reaction exothermic or endothermic Use this result and the Hammond Postulate to predict whether the transition state will be more reactant like or more product like . Compare the geometry of the transition state to that of the reactants and products. Does the Hammond Postulate correctly anticipate the structure of the transition state Explain. 

This final point signifies that the value of a in the rate-equilibrium relationship (2) is not constant but decreases as the reaction becomes increasingly exothermic. It should be noted however that since the Bell- Evans-Polanyi model and the Hammond postulate are couched in energy terms the assumption that free energy changes (AG°) are proportional to energy changes (A °) is inherent in eqns (1) and (2). 

Problem 16.5 Use resonance theory and the Hammond postulate to explain why 3-chioro-1-propene (CH2=CHCH2CI) is more reactive than 1-chloropropane (CH3CH2CH2CI) in Sn1 reactions. 

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. 

The Bell-Evans-Polanyi relationship and the Hammond postulate (see Section 3.3) provide a basic framework within which to discuss structure-reactivity relationships. The Bell-Evans-Polanyi equation implies that there will be a linear relationship between and the C-H BDE. 

The Marcus relation and the Hammond postulate. According to Equation (9.18), electron-transfer reactions resemble proton-transfer reactions in respect of the way that the free energy of activation (AG, ) is affected by the observed free energy of reaction (AGp, ). It follows from Equation (9.18) that the more negative is AG jj (i.e., the higher is ATobs), the lower will be AG, , i.e., the higher will be the rate constant obs- The more exergonic... 

---