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Unformatted text preview: Alkenes: Structure and Reactivity 6.10 - T he H a m mond Postu l a te Summary of electrophilic addition reactions: o Electrophilic addition to an unsymmetrically substituted alkene gives the more highly substituted carbocation intermediate. A more highly substituted carbocation forms faster than a less highly substituted one and, once formed, rapidly goes on to give the final product o A more highly substituted carbocation is more stable than a less highly substituted one. That is the stability order of carbocations is tertiary > secondary > primary > methyl Carbocation stability is determined by the free-energy change ( G) and the reaction rate is determined by the activation energy. The two values arent directly related, but they have an intuitive relationship. Generally, the more stable intermediate forms faster than the less stable one. Hammond Postulate The structure of a transition state resembles the structure of the nearest stable species (relationship between reaction rate and...
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