Energy Diagrams and kinetics
Major concepts
 A reaction will only occur if the rate determining step is kinetically possible
 A catalyst speeds up a reaction by lowering the activation energy of key step(s) in the
mechanism
 Intermediates that are lower in energy will tend to form faster because the activation energy
needed to form that intermediate is lower.
 The major product formed is generally the one that forms faster (the one that goes through the
lower energy rate-determining step)

Vocabulary
 Transition state
 Reaction intermediate
 Rate determining step
 Kinetics
 Carbocation stability
Students should be able to:
 Draw an energy diagram for a multistep reaction mechanism, and indicate intermediates and
transition states
 Use an energy diagram to show how an acid catalyst makes the addition of water to an alkene
faster
 Use an energy diagram to show why the Markovnicov product is the major product in an
addition reaction
Daily Problems
1. What are the relative energies of the starting materials, products, and intermediates in this
mechanism? Draw an energy diagram for this mechanism, assuming the first step is rate limiting.
2. Draw an energy diagram for a 2-step mechanism with a high-energy intermediate that is
endothermic. (Assume its first step is the rate determining step.)
3. Draw an energy diagram for a spontaneous three-step reaction mechanism in which the
intermediates are high energy intermediates and the second transition state is the highest energy TS.
Which step is rate determining?
4. Draw energy diagrams for mechanisms A and B for the addition of water to propene. (Be sure to
consider the relative stabilities of all the compounds and draw them with correct relative energies.)
Which reaction works? What effect does the catalyst have on the reaction? Refer to your energy
diagrams to answer these questions.
5. A. Draw an energy diagram for just the first step (the rate determining step) of the addition of HCl to
propene to form the primary carbocation. B. Draw a similar diagram for formation of the secondary
carbocation. C. Put parts A and B together on the same diagram, taking into consideration that the
starting material is identical in both cases. D. How does this energy diagram explain why the
Markovnicov product is formed rather than the primary alkyl chloride?
Cumulative problems
6. Draw mechanisms for the formation of Product A and Product B. Explain why Product A is formed,
but not product B using an energy diagram.
7. When HBr is added to 1,1,1-trifluorobut-2-ene, two possible carbocation intermediates could form.
Draw both possible intermediates. Which one is more stable? Draw the major product of the reaction.
8. When treating a diene with HCl, only one potential intermediate cation is formed, and not the other.
Explain.
HCl
not formed
Once this intermediate is formed, it can lead to two products. Explain, and give a mechanism.
HCl
Cl
Cl
Extension problem
9. Based on the bonding in this reaction, in which direction would you predict the equilibrium of this
reaction to lie?
If, during the course of this reaction, water is constantly removed so that it can’t react to go back to
starting material, the equilibrium of the reaction would be force to the ______________.