The isomerization of cyclohexene oxide (CHO) to 2-hydroxy-3,4-epoxycyclohexanone (HEC) can be carried out either uncatalyzed or in the presence of an acid catalyst. Standard-state free-energy data at 298 K are summarized below (all values in kJ mol⁻¹ relative to CHO):
• Uncatalyzed transition state: +190
• Acid-catalyzed transition state: +90
• Product HEC: –35
(a) On a single set of axes, draw a qualitative reaction coordinate diagram comparing the uncatalyzed and acid-catalyzed pathways. Clearly label all key features and numerical energy differences.
(b) Explain how the presence of the acid catalyst alters the kinetic parameters of the reaction while leaving the thermodynamic parameters unchanged. Your explanation should address both activation energy and ΔG∘.
(c) A student claims that the catalyst shifts the position of equilibrium toward HEC. Evaluate this claim and support your reasoning with the data above and appropriate thermodynamic principles.
(d) Describe how the rate and the extent of conversion to HEC would be expected to change if the reaction were conducted at 298 K with the catalyst removed but the temperature raised to 400 K instead. Justify your predictions using both kinetic and thermodynamic arguments.