Substituent Effects. XVIII. The Resonance Demand in the Acetolysis of Neophyl Brosylates

Abstract

Abstract The substituent effect in the acetolysis of neophyl brosylates was analyzed statistically based on the Yukawa–Tsuno LArSR equation. Though the Brown ρ+σ+ equation did not provide a linear correlation, the LArSR equation gave an excellent linear correlation with an r value of 0.57, substantiating our basic LArSR concept of varying resonance demands with different systems. For a statistical examination of the reliability of this nonunity r value, the change in the standard deviation of the LArSR correlation was followed as a function of varying r by an iterative least-squares method. The r value of the neophyl solvolysis must have sufficient statistical significance to distinguish between the LArSR and simple Brown ρ+σ+ correlations of this system. The significance of the best-fit correlation was found to strongly depend upon the number and combination as well as the range of the effective substituents. The study was extended to various aryl-assisted processes of complex mechanisms, solvolyses of 2-arylethyl, 2-aryl-1-methylethyl, 2-aryl-1-methylpropyl, and (1-arylcyclobutyl)methyl arenesulfonates. A precise dissection analysis of non-crossover kΔ and ks processes has been realized by the Gauss–Newton type nonlinear least-squares method based on the assumption of LArSR correlations for both processes. The generality of the unique rΔ value of neophyl solvolysis was verified regarding these β-aryl-assisted processes. The substituent effect on the kΔ process can be characterized far more appropriately in terms of the \barσΔ of r=0.6, rather than σ+ of r=1.00.