ENTHALPIES OF HYDROGEN BONDING AND CHANGES IN DELTANUOH FOR A SERIES OF ADDUCTS WITH SUBSTITUTED PHENOLS

The enthalpies of adduct formation for a series of substituted phenols with various Lewis bases have been calorimetrically determined. The acids studied now include C6H5OH, p-t-G4H9C6H4-OH, p-ClC6H4OH, and m-CF3C6H4OH. The frequency shifts of the phenols upon complexation, ∆vOH, have been measured, and the values for all of the phenols studied are found to lie on the same plot of -∆H vs. ∆vO-H. The E and C parameters (vide infra) have been calculated for each of the phenols, and the measured enthalpies are nicely incorporated into this correlation. For a given donor, the enthalpy of adduct formation with this series of phenols correlates with the Hammett substituent constant of the phenol. A procedure is reported which makes it possible to predict enthalpies of adduct formation for any meta- or para-substituted phenol whose Hammett substituent constant is known with any donor that has been incorporated into the E and C correlation. The procedure is tested by application to p-FC6H4OH. The enthalpies predicted this way can be checked with those measured from the O-H frequency shift correlation, eliminating the need for a tedious calorimetric determination of the enthalpy of adduct formation. The accuracy of the predicted enthalpy is as good as the accuracy of the experimental measurement, ±0.2 kcal mole-1. © 1969, American Chemical Society. All rights reserved.