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Selectivity of nitro versus fluoro substitution in arenes in their reactions with charged O ‐ and S ‐nucleophiles
Author(s) -
Khalfina Irina A.,
Vlasov Vladislav M.
Publication year - 2007
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1146
Subject(s) - chemistry , nucleophile , nitro , substituent , nitrobenzene , selectivity , substitution reaction , medicinal chemistry , enthalpy , stereochemistry , organic chemistry , alkyl , catalysis , thermodynamics , physics
The relative mobility of nitro and fluoro substituents in 1,3‐dinitro‐ and 1‐fluoro‐3‐nitrobenzenes, 3,5‐dinitro‐ and 3‐fluoro‐5‐nitrobenzotrifluorides under the action of the nucleophiles (2ArYH)·K 2 CO 3 and ArY − K + in solution and the nucleophiles ArYH·K 2 CO 3 (Y = O, S) under heterogeneous conditions was studied by a competitive method in DMF at 40–140 °C. The unique dependences of ΔΔ H ≠ on ΔΔ S ≠ and ΔΔ H ≠ on ΔΔ G ≠ were determined for all the substrates and nucleophiles. The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions studied: (i) substituent effects in the nucleophiles (2ArYH)·K 2 CO 3 and ArYH·K 2 CO 3 on the activation entropies suggest that the entropy favours the displacement of nitro group; (ii) the negative signs of ΔΔ H ≠ and ΔΔ S ≠ for the reactions of the nucleophiles ArY − K + indicate that the enthalpy determines the displacement of nitro group. It is concluded that the selectivity of the reactions with aryloxide and arylthioxide ions cannot be explained by the hard–soft acid–base principle only. Copyright © 2007 John Wiley & Sons, Ltd.