Ch_322b_15.10

Ch_322b_15.10 - Chapter 15.10 lecture note

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Theory of Substituent Effects The reactivity of substituted benzenes in electrophilic aromatic substitution is determined by the electronic influence of the substituent on the developing carbocation intermediate- the arenium ion . S S is some substituent + E + RDS An electrophile attacks o,m, or p to a substituent . ! + H E ! + S transition state [the developing arenium ion} H E S + arenium ion intermediate When S is electron-releasing , it stabilizes the arenium ion intermediate, and is expected to decrease the energy of the transition state relative to the reaction of benzene. When S is electron-withdrawing , it should destabilize the arenium ion intermediate, and is expected to increase the energy of the transition state relative to the reaction of benzene.
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A Comparison of the RDS for Benzene and Substituted Benzenes in Electrophilic Aromatic Substitution Free Energy NO 2 + E + + E + CH 3 + E + The major electronic effect of the substituent (electron-withdrawing or electron-donating) is on the
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Ch_322b_15.10 - Chapter 15.10 lecture note

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