Dediazoniation of Arenediazonium Ions. 24. Dual and Triple Substituen Parameter Evaluation of Competitive Heterolytic and Homolytic Dediazoniations of Diazonium Ions Complexed with 18-Crown-6 Ether

Article abstract of DOI:10.1021/jo00389a033

The dediazoniation of eight para-substituted benzenediazonium ions in 1,2-dichloroethane is a heterolytic reaction.The corresponding 18-crown-6 ether complexes of these diazonium ions, however, react also homolytically.The rate constants for heterolytic dediazoniation of the free diazonium ions (k₁), the rate constants for competitive heterolytic and homolytic dediazoniation of the crown ether complexed diazonium ions (k₃ and k₄, respectively), and the equilibrium constants for formation of the diazonium ion-crown ether complexes (K) were correlated with dual substituent parameter (DSP) treatments.A comparison has been made with the following substituent constants: Taft's original DSP substituent constants, Taft's triple substituent parameter constants (TSP) based on gas-phase reactions (1987), Charton's modified DSP constants, and the original (1968) and revised (1983) constants proposed by Swain.The reaction constants with the best (smallest) standard deviations and confidence limits and the highest regression coefficients are obtained with the substituent constants of Taft (both the original and the new gas-phase constants) and those of Charton.The heterolytic dediazoniation is characterized by clearly opposing signs of the field and resonance reaction constants ( and ), in contrast to the homolytic dediazoniations.The DSP treatments currently available do not provide meaningful results with homolytic dediazoniation.