Crash Course Organic Chemistry: Reaction Kinetics and Thermodynamics
Introduction
- Presenter: Deboki Chakravarti
- Organic chemicals are present in many smells around us.
- Example: Limonene in lemons converts to alpha-terpineol with a lilac smell through enzyme-catalyzed reaction.
- To understand such reactions, concepts like reaction kinetics, thermodynamics, spontaneity, and free energy are essential.
Key Concepts in Organic Reactions
Useful Chemical Reactions
- Must have more products than reactants.
- Reaction should occur at a reasonable speed.
- Thermodynamics: Relates to energy and reaction progress.
- Kinetics: Relates to the rate of reaction.
Review of Key Thermodynamics Concepts
- ΔH (Enthalpy): Change in heat at constant pressure.
- Exothermic: Reaction gives off heat (Negative ΔH).
- Endothermic: Reaction absorbs heat (Positive ΔH).
- ΔS (Entropy): Degree of disorder or randomness in the system.
- Example: Increase in entropy when a compound changes from a ring to a chain.
- ΔG (Gibbs Free Energy): Predicts spontaneity of a reaction.
- Negative ΔG: Spontaneous reaction.
- Positive ΔG: Non-spontaneous reaction.
- Equation: ΔG = ΔH - TΔS
Equilibrium and Reaction Rates
- Equilibrium Constant (K): Ratio of products to reactants at equilibrium.
- Large K: More products.
- Small K: More reactants.
- Relationship: ΔG = -RTlnK
- Negative ΔG → Large K; Positive ΔG → Small K.
Energy Diagrams
- Y-axis: Reaction energy (ΔH or ΔG).
- X-axis: Reaction progress from reactants to products.
- Transition State: Peak of the diagram.
- Activation Energy: Energy required to start the reaction.
- Higher activation energy → Slower reaction.
Reaction Example: But-1-ene and Hydrogen Bromide
- Endothermic reaction forming primary or secondary carbocations.
- Secondary carbocations more stable due to less energy needed for formation.
Multi-Step Reactions
- Example: Reaction between 2-methylprop-2-ene and methanol forming MTBE.
- Involves sulfuric acid as a catalyst.
- Path includes multiple intermediates and transition states.
- Intermediates: Have full charges and bonds.
- Transition States: Partial charges and bonds.
Catalysts in Reactions
- Catalysts speed up reactions without being consumed.
- Lower the activation energy in energy diagrams.
Conclusion
- Reviewed thermodynamics, enthalpy, entropy, Gibbs free energy.
- Studied free energy diagrams, intermediates, and transition states.
- Explained catalysts' role in reducing activation energy.
- Upcoming episodes to cover more on addition reactions.
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