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Mechanism of nucleophilic fluorination promoted by bis‐ tert ‐alcohol‐functionalized crown‐6‐calix[4]arene
Author(s) -
Pliego Josefredo R.
Publication year - 2018
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.25648
Subject(s) - chemistry , nucleophile , fluoride , molecule , reagent , hydrogen bond , ion , caesium , alcohol , solvent , nucleophilic substitution , dipole , medicinal chemistry , alkyl , inorganic chemistry , computational chemistry , organic chemistry , catalysis
Theoretical calculations were performed to elucidate the ability of the recently reported bis‐ tert ‐alcohol‐functionalized crown‐6‐calix[4]arene (BACCA) molecule to promote nucleophilic fluorination of alkyl mesylates with cesium fluoride reagent. It was found that a similar structure, named BACCAt, can separate the cesium fluoride ion pair in tert ‐butanol solution. This separation has a free energy cost, even considering the double hydrogen bonds with the fluoride ion. The solvent has an important effect on the stabilization of this complex, due to interaction with the high dipole moment of the separated ion pair. The observed rate acceleration effect involves a structure with double hydrogen bonds between the BACCAt and the centers of negative charges of the S N 2 transition state. The predicted free energy barrier of 27.3 kcal mol −1 is in excellent agreement with the estimated experimental value of 26.2 kcal mol −1 .