CHEM261 Lecture Notes - Lecture 32: Charge Conservation, Acid Dissociation Constant, Alkene

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Resonance Notes
Resonance molecule represented by more than one lewis structure but differing in
only placement of electron.
Resonance is not the true structure because it is not in chemical equilibrium, it does not
fluctuate. Therefore the true structure is the resonance hybrid.
Resonance structures used because Lewis structures is localized therefore resonance
helps delocalized.
Resonance hybrid has lower potential energy therefore more stable.
Rules for drawing resonance:
Only move multiple bonds and lone pairs. NOT single bonds.
Atom position stays the same.
Proper lewis structure (no pentavalent carbon)
Charge conservation -- sum of formal charges must be the same.
Receptor of electron pairs are positive charged atoms, EN atom, or atom with multiple
bonds.
Drawing resonance for cation One arrow changed at a time. Electron pair moves
towards the positive formal charge.
Drawing resonance for anion Move two arrows at a time. Electron pair moves away
from negative charge. Note: Atom to bond, bond to atom.
Negative charge is most favoured on the most EN atom.
When there is a positive charge remaining, the positive charge is favoured on the
resonance with full octet.
Charge separation (when compound is neutral breaks to positive and negative). It is not
favoured.
Types of Chemical Reactions
1. Acid-Base Reactions (Proton Transfer)
2. Substitution Reaction One element replaces another
3. Elimination Reaction Removal of two elements to form alkene
4. Addition Reaction Addition of two elements to break alkene bond
5. Rearrangement (catalyst) change in carbon skeleton
6. Oxidation (w/ [O] as catalyst) remove Hydrogen to form water
7. Reduction (catalyst) Addition of Hydrogen; Example Ketone Alcohol.
Define
Homolytic cleavage (homolysis) Electron pair splits, each atom takes its own
electrons (half arrows).
Heterolytic Cleavage (heterolysis) One atom takes all and an ion is formed.
Bronsted-Lowry Acid Donates proton.
Bronsted-Lowry Base Accepts proton. Base has a lone pair of electrons to accept
proton.
Organic Reaction Notes
As pKa increases, the acid becomes weaker.
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