Updated January 22, 2022 You know the drill, this is your go-to source for information concerning Organic Chemistry class! Past week's announcements will be saved in their respective quarter tabs.
Week 18 Summary
Chapter 6 - The Proton Transfer Reaction An Introduction to Mechanisms, Thermodynamics and Charge Stability
As a reminder, we are still in Chapter 6 - The Proton-Transfer Reaction. It is comprised of the following sections:
Section 6.1 - An Introduction to Reaction Mechanisms: The Proton-Transfer Reaction and Curved Arrow Notation
Section 6.2 – Chemical Equilibrium and the Equilibrium Constant, Keq
Section 6.3 – Thermodynamics and Gibbs Free Energy
Section 6.4 - Functional Groups and Acidity
Section 6.5 – Relative Strengths of Charged and Uncharged Acids: The Reactivity of Charged Species
Section 6.6 – Relative Acidities of Protons on Atoms with Like Charges
Section 6.7 – Ranking Acid and Base Strengths – The Relative Importance of Effects on Charge
Section 6.8 – Determining Relative Contributions by Resonance Structures
Section 6.9 – Wrapping Up and Looking Ahead
Section 6.10 – Structure of Amino Acids in Solution as a Function of pH
This is a very key chapter and important that you understand it very, very well, since it provides a foundation for the chemical reactions we will learn from here on out. Please take the time to read through it carefully, and do not wait until the last minute to complete the homework problems!
As a reminder as to the various definitions of acids and bases:
Bronsted-Lowry - acids are molecular species that donate protons, whereas bases are species that accept protons.
Arrhenius acids donate protons in aqueous solutions and bases donate hydroxide ions
Lewis acids accept electron pairs, and bases donate electron pairs. Note that the Lewis definition for an acid, then, is not limited to being a "proton donor."
For this chapter, we are principally interested in the Bronsted-Lowry characterization.
This past week you were reminded about equilibrium constants (Keq), and dissociation constants for acids (Ka), and how they are expressed as pKa. Recollect that molecular species with very low pKa values are more acidic than those with higher pKa values.
What to Expect in Week 19
It is easy to get lost in all the material from this chapter, so please make sure you stay on top of reading and the homework assignments.
This week you will be introduced to the Henderson-Hasselbalch equation. Examine the graph at left - the most important thing to know about this is when an acid's pH is equal to its pKa, then 50% of it is dissociated. While I don't expect you to know the details behind this equation, you do need to understand what an acid's pKa means.
We will also be introduced to thermodynamics and what is called Gibb's free energy. Take a look at the free-energy diagram below left. Note that it plots the energy of the reactants, products, and transition state for a reaction between a base and methyl chloride.
Since the products (methanol and chloride ion) have less energy than the reactants, the reaction is said to be exothermic.
The energy difference between the reactants and the transition state is called the energy of activation. This energy "hill" is what is overcome when chemists use catalysts in reactions (such as heat, a metal, an acid or base).
Week 19 Resources/ Assets
Due to teacher/ student illness and the fact this is a monster of a chapter - we are currently off-schedule!