Simple method for determining of the isokinetic temperature value for the S_NAr reactions in solution

Abstract

The changes of the free energy of activation δΔG ≠ exp and the activation entropy δΔS ≠ in the framework of the isokinetic relationship δΔG ≠ exp versus (T iso − T exp ) δΔS ≠ were explored quantitatively to predict the isokinetic temperature T iso for the aromatic nucleophilic substitution reactions in solution.KEYWORDS activation parameters, isokinetic relationship, isokinetic temperature, reaction mechanism, S N Ar reactions, substituent effects, transition state | INTRODUCTIONSignificant effort in recent decades has been made in the determination of the isokinetic relationship (IKR) in the S N Ar reactions. [1][2][3][4][5][6][7][8][9][10] The existence of this extra-thermodynamic tool infers a possible change in the reaction mechanism at some IKRs, [1] or the reactions occur by identical mechanism at the existence of a single IKR. [11,12] Recently, it was shown the possibility to predict the isokinetic temperature T iso based on the variation in the internal enthalpy of activation, δΔH ≠ int , and also in the parameters δΔS ≠ and δΔG ≠ for the S N Ar reactions of the benzene derivatives at structural changes to the nucleophiles and substrates (Equation 1).[13]The compensation temperature, T comp , is the slope in the linear relationship between the changes of the enthalpy and entropy of activation, ΔH ≠ and ΔS ≠ , for the series of the similar reactions [14] according to Equation 2.It should be noticed that the external part, δΔH solution, [28] in which step k 1 is rate determining. [28,31] Therefore, the analysis of the changes in the free energy of activation, δΔG ≠ , and also the entropy of activation, δΔS ≠