Understanding Acids, Bases, and Reaction Mechanisms with Curved-Arrow Notation
This overview covers essential concepts about acids and bases, focusing on their behavior in electrochemical reactions. It explains the distinctions between Lewis and Bronsted definitions, including how Lewis acids and bases interact through electron pairs. Additionally, it introduces curved-arrow and fish-hook notation for visualizing electron movement in reaction mechanisms. Examples illustrate how acids produce conjugate bases in aqueous solutions and how amphoteric compounds demonstrate both acidic and basic properties. This foundational knowledge is crucial for anyone studying organic chemistry.
Understanding Acids, Bases, and Reaction Mechanisms with Curved-Arrow Notation
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Presentation Transcript
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 from a low-energy orbital, producing the conjugate base. Examples: AlCl3, BF3, H+ Lewis bases donate a pair of electrons to a low-energy orbital, producing the conjugate acid. Examples: OH-, CH3O-, NH3 Bronsted acids donate H+, producing the conjugate base. Examples: HCl, H+ Bronsted bases accept H+, producing the conjugate acid. Examples: OH-, CH3O-, NH3
In aqueous solutions: Acids produceH+ and the conjugate base. Example: CH3COOH = H+ + CH3COO- Bases produceOH- and the conjugate acid. Example: NH3 + H2O = OH- + NH4+ 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 pKa 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 1. 4. 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:
