SOME HYDROGEN-BOND RELATIONS BETWEEN HOMOCONJUGATES AND HETEROCONJUGATES OF PHENOLS AND PHENOLATES IN ACETONITRILE

With the exception of of ortho-substituted phenols, the hydrogen-bond donating capacity with reference to chloride ion of substituted phenols (HA) as indicated by the heteroconjugation constant KfHA·c1 - = [HA • Cl−]/ [HA ·][Cl−] increases with increasing acid strength of HA. The hydrogen-bond accepting capacity of A-, as indicated by K1hr, A-, HR being p-bromophenol, increases with increasing basic strength of A-. This is also true for ortho-substituted phenolate ions. A plot of log KfHA·Cl− vs. the Hammett substituent constants σ yields a straight line with slope of 1.0 except for ortho-substituted phenols, while the plot of log KfHR · A− vs. σ is linear for all phenols tested and has a slope of – 1.28. A value of σ = 1.10 for the o-nitro group was used. The equilibrium constant of the reaction HA2−+ HR·Cl−↔ HA • Cl− + HR • A- was expected and found to be equal to 1, except for 2,6-dinitro-4-chlorophenol. ortho-Substituted phenols form only a monoconjugate HA•Cl−, whereas meta-and para-substituted phenols also form a diconjugate (HA)2Cl−. A plot of pKdHA vs. a yields a straight line, but the plot of (pkdHA)AN vs. (pkdHA)water exhibits considerable scatter. © 1969, American Chemical Society. All rights reserved.