Chemical Structure and Acidity Constant

0 From Clark and Perrin (1964). b A plus sign means that the effect increases the p/fa a minus sign means that the effect decreases the p/fa. 

Let us first consider a simple example, the influence of a chloro-substituent on the pKa of butyric acid  

As illustrated by the chlorobutyric acids discussed above, in saturated molecules inductive effects usually fall off quite rapidly with distance. 

In the next step, we introduce a substituent on the aromatic ring which, through the aromatic -electron system, may develop shared electrons (i.e., through resonance or conjugation ) with the acid or base function (e.g., the -OH or -NH2 group). For 

Another important group of effects are proximity effects. that is, effects arising from the influence of substituents that are physically close to the acid or base function under consideration. Here, two interactions are important intramolecular (within 

---