Acidity in Organic Molecules

The reaction of HA and B to give BH+ and A is the general expression written for acid-base reactions. The acid (HA) reacts with a base (B ) to give the conjugate acid, HB+ (CA) and a conjugate base, A (CB). 

I The hydrogen is transferred to B as a proton (H+). Since the product, HB, is also an acid and A is a base, this reaction is an equilibrium. The position of the equilibrium is directly related to the acidity of HA and the position of this equilibrium is given by the equilibrium constant K, where Xa is used for acid-base reactions. If the electron pair of the base (B) easily removes tbe proton from HA, the equilibrium is shifted to the right. 

Chapter 2. Acids, Bases, Functional Group Exchanges 

Another nontraditional weak acid is the hydrogen on the a-carbon of a ketone such as 2-butanone. When 2-butanone (A) reacts with sodium ethoxide (B), the conjugate base is enolate anion 8 (CB), and ethanol is the conjugate acid (CA). Ethanol is a stronger acid than the ketone and can reprotonate the basic enolate. This shifts the equilibrium back to the left, and the net result is a solution that contains enolate 8, ethanol, unreacted 2-butanone, and NaOEt (sec. 9.2.E). It is important to note that HA does not function as an acid unless a sufficiently strong base (B) is present to remove and accept the acidic proton. If the base under consideration 

When comparing two acids, several factors can be used to evaluate relative acid strength. In an acid-base reaction where acids are on both sides of the equilibrium (A and CA from above), this information can be useful to estimate the position of the equilibrium, which is essentially an estimation of Ka. 

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It is apparent that acidity in organic molecules is influenced by several factors. Among these, inductive effects, solvent effects, and factors that influence the stability of both the acid and the anionic conjugate base are important. The base is obviously important since the strength of an acid is directly dependent on the strength of the base. 

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