1. Organic Chemistry
Chapter 24
4 Edition
th
Paula Yurkanis Bruice
Catalysis
Irene Lee
Case Western Reserve
University
Cleveland, OH

2. Catalyst
A catalyst is a substance that increases the rate of a
reaction without itself being consumed or changed
A catalyst increases the rate of the reaction by lowering
the ∆G‡ of the reaction
A catalyst can decrease ∆G‡ of the reaction by one of
three different ways

3. The Catalyst Converts the Reactant to a Less
Stable Species

4. The Catalyst Stabilizes the Transition State

5. The Catalyst Changes the Mechanism of
the Reaction

6. A catalyst can provide a more favorable pathway for
an organic reaction by:
• increasing the susceptibility of an electrophile to
nucleophilic attack
• increasing the reactivity of a nucleophile
• increasing the leaving ability of a group by
converting it to a weaker base

7. Nucleophilic Catalysis
Both the formation of the acyl imidazole and its
subsequent hydrolysis are both faster than ester
hydrolysis

8. An Acid-Catalyzed Reaction
A proton is donated to the reaction

9. The acid increases the rates of both slow steps of the
reaction

10. In specific-acid catalysis, the proton is fully transferred
before the slow step of the reaction
In general-acid catalysis, the proton is transferred during
the slow step of the reaction

11. Compare Specific-Acid Catalysis with General-
Acid Catalysis

12. A specific-acid must be a strong acid
A general-acid can be a weaker acid

13. Base Catalysis
A base catalyst increases the rate of the reaction by
removing a proton from the reaction
specific-base catalyzed dehydration

14. The rate of the reaction is accelerated by stabilization
of the transition state
In specific-base catalysis, the proton is completely
removed before the slow step of the reaction

15. general-base catalysis
In general-base catalysis, the proton is removed during
the slow step of the reaction

16. Metal-Ion Catalysis
A. The metal ion increases the susceptibility of electron
attack
B. The metal ion makes the leaving group a weaker base
C. The metal ion increases the nucleophilicity of water

17. An Example of a Metal-Ion-Catalyzed Reaction

18. Metal-Ion-Catalyzed Decarboxylation

19. Metal-Ion-Catalyzed Ester Hydrolysis
The metal-bound hydroxide is a better nucleophile than
water
The metal ion also decreases the basicity of the leaving
group

21. The relative rates are also called the effective molarity
The effective molarity is the advantage given to a
reaction
The relative rate of reactant D is higher than the relative
rate of B because the groups in D are less apt to adopt
an unfavorable conformation for the reaction

23. Putting a reacting group and a catalyst in the same
molecule increases the rate of the reaction
Intramolecular catalysis is also known as anchimeric
assistance

24. The trans isomer reacts much faster than the cis isomer

26. The rate of phenyl acetate hydrolysis is enhanced by
an intramolecular general base catalysis

27. In the presence of nitro groups, the ortho-carboxyl
substituent acts as an intramolecular nucleophilic
catalyst

28. An Intramolecular Metal-Ion Catalysis

29. Most Biological Catalysts Are Enzymes
The reactants are called substrates
The substrate specifically fits and binds to the active site

30. Hexokinase undergoes a conformational change upon
binding to a substrate
red: before substrate-binding
green: after substrate-binding

31. Important Features that Contribute to the
Catalytic Ability of Enzymes
• Reacting groups are brought together at the active site
in the proper orientation for reaction
• Some of the amino acids in the enzyme serve as
catalytic groups; many enzymes have metal ions as
catalysts
• Groups on the enzyme can stabilize the transition state
of the reaction

32. Carboxypeptidase A catalyzes the hydrolysis of the
C-terminal peptide

33. The binding pocket at the active site of serine proteases
dictates substrate specificity

34. The Proposed Reaction Mechanism of a
Serine Protease

35. Lysozyme Is an Enzyme that
Destroys Bacterial Cell Walls

36. The amino acids at
the active site of
lysozyme are
involved in binding
the substrate

37. The Proposed Reaction Mechanism
for Lysozyme

38. The pH-rate profile of an enzyme is a function of the
pKa values of the catalytic groups in the enzyme
a group is a group is
catalytically catalytically
active in its basic active in its acidic
form form

39. Glucose-6-phosphate Isomerase