| Popis: |
Substituent and temperature effects on the equilibrium constants for the triethylamine-catalyzed acyl exchange reactions of N-(substituted benzoyl)-O-acetyl-o-aminophenols have been investigated by 1H NMR spectroscopy. It was found that the standard enthalpy change ΔH° in acyl exchange processes, estimated from temperature dependence of the equilibrium constant, correlates well with the standard free energy change ΔG° which was used as a measure of the relative stability of isomer pairs, while the standard entropy change ΔS° is approximately constant (−6 ± 2 J K−1 mol−1) irrespective of the substituents in benzoyl introduced. The finding of enthalpy-controlled acyl exchange reactions confirms that the relative stability of a given isomer pair is determined by the difference in electrostatic force of attraction between the amide nitrogen with a partial positive charge and the ester carbonyl oxygen having a partial negative charge in both isomers. |
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