Effects of ion-pairing and hydration on the SNAr reaction of the F− with p-chlorobenzonitrile in aprotic solvents

文献情報

出版日 2007-12-21

DOI 10.1039/B716159J

インパクトファクター 3.676

著者

Josefredo R. Pliego, Jr, Dorila Piló-Veloso

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要旨

Theoretical ab initio calculations including liquid phase optimizations were used to investigate the SNAr reaction of the fluoride ion with p-chlorobenzonitrile in dimethyl sulfoxide solution. The effect of the counter ion and hydration of the fluoride ion with one water molecule was analyzed. The calculations indicate that the gas-phase SNAr reaction is more favorable than the corresponding SN2 reactions involving fluoride ion and 2-chlorobutane. However, the substantially higher solvent effect on the SNAr reaction makes the nucleophilic substitution on the aromatic ring less favorable than the aliphatic reaction in the liquid phase. For the anhydrous tetrabutylammonium fluoride system, the theoretical free energy barrier of 22.1 kcal mol−1 is close to the experimental one of 24.4 kcal mol−1. The smaller tetramethylammonium cation strongly associates with the fluoride ion and increases the barrier by 5 kcal mol−1. Similarly, just one water molecule hydrating the fluoride ion has the same effect. An analysis of the reaction involving the ion pair and the free anion in different polarity media predicts an unexpected behavior and indicates there is an ideal solvent polarity for each counter ion.

掲載誌

Physical Chemistry Chemical Physics

CiteScore: 5.5

自己引用率: 10.3%

年間論文数: 3036

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