The Transition State of the Acid Catalyzed Alkoxide Ion Departure from Meisenheimer Complexes (1)
Alkoxide ion departure from Meisenheimer complexes of the 1,1-dialkoxy-2,6-dinitro-4-X-cyclohexadienate type is catalyzed by pyridinium ions and by the hydronium ion. Bronsted α values which vary between 0.35 and 0.65 decrease when the alkoxy group becomes more electron withdrawing and increase when the X-substituent is made more electron withdrawing. This is inconsistent with a mechanism where proton transfer is rate limiting but in complete agreement with a concerted mechanism of acid catalysis as shown with the help of More O’Ferrall-Jencks energy diagrams.
KeywordsTransition State Proton Transfer Reaction Coordinate Alkoxy Group Energy Diagram
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