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Gas‐phase acylium ion transfer reactions mediated by a proton shuttle mechanism
Author(s) -
Fileti Eudes E.,
De Oliveira Anselmo E.,
Morgon Nelson H.,
Riveros José M.
Publication year - 2011
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.22746
Subject(s) - chemistry , exothermic reaction , protonation , ion , acetic acid , reaction mechanism , oxonium ion , computational chemistry , proton , methanol , photochemistry , stepwise reaction , reaction rate constant , organic chemistry , catalysis , quantum mechanics , order of reaction , physics , kinetics
Abstract The mechanism and the energy profile of the gas‐phase reaction that mimics esterification under acidic conditions have been investigated at different levels of theory. These reactions are known to proceed with rate constants close to the collision limit in the gas‐phase and questions have been raised as to whether the typical addition‐elimination mechanism via a tetrahedral intermediate can explain the ease of these processes. Because these reactions are common to many organic and biochemical processes it is important to understand the intrinsic reactivity of these systems. Our calculations at different levels of theory reveal that a stepwise mechanism via a tetrahedral species is characterized by energy barriers that are inconsistent with the experimental results. For the thermoneutral exchange between protonated acetic acid and water and the exothermic reaction of protonated acetic acid and methanol our calculations show that these reactions proceed initially by a proton shuttle between the carbonyl oxygen and the hydroxy oxygen of acetic acid mediated by water, or methanol, followed by displacement at the acylium ion center. These findings suggest that the reactions in the gas‐phase should be viewed as an acylium ion transfer reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010