Cross-interaction constants as a measure of the transition state structure. Part 11. Solvolyses of 1-phenyl-2-propyl benzenesulphonates

Abstract

The solvolyses of 1-phenyl-2-propyl benzenesulphonates (PPBs) have been investigated in methanol–acetonitrile mixtures and in hexafluoropropan-2-of (HFIP). The transition state structure has been discussed using various selectivity parameters, especially with the cross-interaction constants, ρ_YZ and λ_YZ, between substituents in the substrate (Y) and in the leaving group (Z). It has been found that the solvolysis proceeds by the solvent-assisted pathway, k_s, in methanol, whereas in HFIP PPBs solvolyse via the aryl-assisted pathway, k_Δ. The only exception was the p-MeO substituent, which deviates positively in methanol from the log k_svs. σ plot due to participation of the aryl-assisted path and negatively in HFIP from the log k_Δvs. σ_(neophyl) plot due to deactivation by hydrogen bonding of the methoxy oxygen in the acidic solvent. The two distinctive high values of ρ_YX provided evidence for the strongly bound transition states in the two processes, k_s and k_Δ, with a relatively low degree of bond breaking.