The Substituent Effect. V. NMR Chemical Shifts of Hydrogen-bonding Hydroxyl Proton of Phenols in DMSO

The chemical shifts of the hydrogen bonded OH proton of m- and p-substituted phenols, and 4-substituted 2-cresols, 3-cresols, and 2,6-xylenols were determined in DMSO. The effects of substituents on the hydroxyl chemical shift of these series were correlated linearly with each other (correlation coefficient>0.999), except for the bulky planar substituents in the 3-cresol series which may be subject to the steric loss of their coplanarity with the benzene ring. The substituent effects were treated successfully with the equation, Δδ=ρ(σ0+r−ΔσR−). The phenol series gave r−=0.673 and ρ=1.530. The same r− value appeared to be applicable to all the other series with negligible changes in the ρ value. Deviations from the correlation of particular substituents, in particular those having acidic hydrogen, were attributed to the modification of the electronic nature of substituents arising from the strong substituent-DMSO interaction.