Effect of Substituents on Acidity and Basicity

The effect of substituents on the acidity and basicity of aniline, and on the acidity of phenol, is given, respectively, by the energy changes in reactions 4-6. 

It is possible to break down the effect of substituents on acidity or basicity into the effect on the charged species on the one hand and on the corresponding neutral species on the other. For example, the effect of substituents on the acidity of aniline (reaction 4) is given by the difference between the interaction energies for the appropriate substituted anilide ion (reaction 7)  

Such a breakdown is useful in determining the origin of the substituent effect. 

Theoretical and gas-phase experimental results for the effect of substituents on phenol acidity (10) are listed in Table 24. Similar data for aniline acidity and basicity are given in Table 25. In general, there is good agreement between the available experimental values and the theoretical results, allowing greater confidence in those theoretical values which at present remain experimentally unverified. 

Effect of Substituents on Acidities of Phenols (kcal mole ) 

---