Influence of Steric Factors on the Structure and Physicochemical Properties of Monohydric Phenols

The specificity of a series of chemical properties of sterically hindered phenols depends greatly on their structure. In the series of 2,6-di-t-alkylphenols in which conjugation of the aromatic ring and hydroxyl group is retained (insignificant departure from coplanarity) the C–O–H bond system is subjected to some deformation due to the bulky o-alkyl groups (a steric effect), which is reflected in the energy of homolytic breaking of the O–H bond and the physicochemical parameters of these phenols. The unusual nature of the spectral characteristics (ultraviolet, infrared, and NMR) of sterically hindered phenols is due to the steric effect of the ortho-substituent. For the same reason these compounds do not form self-associates; the hydrogen bond is somewhat stretched and weaker. Steric effects also play a decisive part in the reduction of acidity of sterically hindered phenols, preventing the solvation of the anion formed. For all the examples considered data are given on the effect of a para-substituent on the physicochemical parameters of the phenols. 98 references.