Neighboring Group Participation in Solvolysis. X. Dissection of Ar1-5 and Ar2-6 Pathways in Trifluoroacetolysis of 4-Arylbutyl 6-Methyl-2-naphthalenesulfonates

Article abstract of DOI:10.1246/bcsj.53.2348

Trifluoroacetolysis rates and products were determined for eleven 4-(m- and p-substituted phenyl)butyl 6-methyl-2-naphthalenesulfonates.Most substrates solvolyze predominantly or even exclusively with aryl assisted (k_Δ) pathway.Dissection of k_Δ into Ar₁-5 and Ar₂-6 components was performed by means of quantitative 13C NMR study of suitably labeled p-methyl and p-fluoro derivatives; the results were 32.4percent Ar₁-5 and 67.6percent Ar₂-6 for the former and 43.3percent Ar₁-5 and 56.7percent Ar₂-6 for the latter.For other substrates the dissection was carried out by postulating two independent linear free energy relationships (LFER) for the two pathways determined by the above four partial rates.Ar₂-6 is much prefered over Ar₁-5 through the series; for the unsubstituted derivative 90.6percent Ar₂-6 vs. 9.4percent Ar₁-5 was determined.A completely different approach by means of non-linear regression analysis of k_Δ as a sum of two independent LFER gave fairly different and rather unsettled results, limitations of such an approach being suggested.The characteristics of remote aryl participation are discussed based on the above data.