CHEM250 Thermodynamics and Aldols

Reaction profile

Exothermic (enthalpy)

* Energy released (favored)
* Making bonds
* -ΔH

Endothermic (enthalpy)

* Energy absorbed (disfavored)
* Breaking bonds
* +ΔH

Entropy

* -ΔS: degrees freedom decrease (disfavored)
* +ΔS: degrees freedom increase (favored)

Gibbs Free Energy

ΔG = ΔH - TΔS

\
* -ΔG: favored reaction, exergonic
* +ΔG: disfavored reaction, endergonic

If a reaction is **reactant** favored, a _____ base was used.

weak

If a reaction is **product** favored, a _____ base was used.

strong

Using a weak base results in how much enolate anion being formed?

little

Using a strong base results in how much enolate anion being formed?

lots

Le Chatelier’s Principle

when a system experiences a disturbance (such as concentration, temperature, or pressure changes), it will respond to restore the ratio of products to reactions (Keq) to the equilibrium set value.

Reversible reaction

* -20 kJ/mol < ΔGrxn < 20 kJ/mol
* 10^-3 < keq < 10^3

Irreversible, product favored reaction

* ΔGrxn < 20 kJ/mol
* keq > 10^3

Irreversible, reactant favored reaction

* ΔGrxn > 20 kJ/mol
* keq < 10^-3

List two ways that you can push a reaction with a small ΔG to products.

1. Add more reactants
2. Remove the products as the reaction is occurring

List the bases that will irreversibly and completely convert an aldehyde or ketone into an enolate.

* LDA
* NaH