Acids and Bases

Required background: 1. Organic structures 2. Electrolytic dissociation Essential for: Writing and understanding reaction mechanisms

1. Acids and Bases 2. Curved-Arrow notation and Fish-hook notation

Lewis acids accept a pair of electrons, producing the conjugate base. Examples: AlCl 3, BF 3, H + Lewis bases donate a pair of electrons, producing the conjugate acid. Examples: OH -, CH 3 O -, NH 3 Bronsted acids donate H +, producing the conjugate base. Examples: HCl, H + Bronsted bases accept H +, producing the conjugate acid. Examples: OH -, CH 3 O -, NH 3

In aqueous solutions: Acids produce H + and the conjugate base. Example: CH 3 COOH = H + + CH 3 COO - Bases produce OH - and the conjugate acid. Example: NH 3 + H 2 O = OH - + NH 4 + Acids react with bases and produce a salt (which can be another base at the same time) and water (which also can act as an acid). Example: Most of the compounds exhibit both acidic and basic properties. Such compounds are called amphoteric compounds. This equilibrium is shifted toward the weaker acid and the weaker base. A stronger acid has a lower value of pK a and a weaker conjugate base.

1. Acids and Bases 2. Curved-Arrow notation and Fish-hook notation

The curved arrow denotes displacement of a pair of electrons (and nothing else!). If the starting structure and curved arrows are shown, you need to follow four steps to figure out the structure of the reaction product: 1. If the space between two atoms loses electrons, one covalent bond breaks. 2. If the space between two atoms gains electrons, one covalent bond forms. 3. If any atom loses electrons, its charge increases by If any atoms gains electrons, its charge decreases by 1. Example:

The fish-hook arrow denotes displacement of one electron (and nothing else!). If the starting structure and fish-hook arrows are shown, you need to follow two steps to figure out the structure of the reaction product: 1. If the space between two atoms loses two electrons, one covalent bond breaks. 2. If the space between two atoms gains two electrons, one covalent bond forms. Example: