Ø The Brønsted-Lowry Definition of Acids and Bases - Acid is a substance that can donate (or lose) a proton; Base is a substance that can accept (or remove) a proton.
Conjugate acid: the molecule or ion that forms when a base accepts a proton.
Conjugate base: the molecule or ion that forms when an acid loses its proton.
Ø The Lewis Definition of Acids and Bases- Acid: electron-pair acceptor; Base: electron-pair donor.
Predicting the Strength of Bases: The stronger the acid, the weaker will be its conjugate base. The larger the pKa of the conjugate acid, the stronger is the base.
Predicting The Outcome of Acid-Base Reactions: Acid-base reactions always favor the formation of the weaker acid and the weaker base.
The Relationship Between Structure and Acidity
The strength of an acid depends on the extent to which a proton can be separated from it and transferred to a base.Breaking a bond to the proton Þ the strength of the bond to the proton is the dominating effect.
The Acidity of Carboxylic Acids
Carboxylic acids are much more acidic than the corresponding alcohols: pKas for R–COOH are in the range of 3-5;.pKas for R–OH are in the range of 15-18.
An Explanation Based on Resonance Effects
Resonance stabilized acetate anion: The greater stabilization of the carboxylate anion (relative to the acid) lowers the free energy of the anion and thereby decreases the positive free-energy change required for the ionization. Any factor that makes the free-energy change for the ionization of an acid less positive (or more negative) makes the acid stronger.
An Explanation Based on Inductive Effects
The inductive effect of the carbonyl group (C=O group) is responsible for the acidity of carboxylic acids.
Organic Compounds as Bases
An organic compound contains an atom with an unshared electron pair is a potential base. The p bond of an alkene can act as a base.