NUCLEAR MAGNETIC RESONANCE STUDIES OF ORTHO-SUBSTITUTED PHENOLS IN DIMETHYL SULFOXIDE SOLUTIONS . ELECTRONIC EFFECTS OF ORTHO SUBSTITUENTS

The relative chemical shifts of OH in ortho-substituted phenols (Δδo) in dimethyl sulfoxide (DMSO) solutions are linearly related to those for para-substituted phenols (ΔδP), are apparently free of steric effects, and afford an excellent measure of electronic effects of ortho substituents. The strong intermolecular hydrogen bond between the phenolic OH and DMSO is apparently oriented away from a single ortho substituent so that proximity interactions are minimal; 2,6-disubstituted phenols do exhibit serious steric interactions even in DMSO solution. The ΔδP values are linearly correlated with Hammett πp− constants, and, from the equation for this line (π− = 0.720Δδ – 0.038) ortho-substituent constants (πo−) for 32 substituents have been assigned. The oacetyl and o-nitro substituents do not fit this correlation because of intramolecular hydrogen bonding. The new ortho-substituent constants are shown to correlate successfully the reactivity data for ortho-substituted compounds in 29 reaction series. © 1969, American Chemical Society. All rights reserved.