Organic Chemistry MCAT Practice Exam

What environmental factor can influence the selectivity of kinetic and thermodynamic enolates?

1. Concentration of reactants

2. Temperature

3. pH of the solution

4. Presence of catalysts

The correct answer is: Temperature

The selectivity of kinetic and thermodynamic enolates is significantly influenced by temperature due to its impact on the energy of the system. Kinetic enolates are formed preferentially at lower temperatures because the reaction conditions favor the formation of products through a fast, lower-energy pathway. At these temperatures, the reaction is sometimes not given enough time to reach equilibrium, leading to the predominance of the less stable, more rapidly formed enolate. Conversely, thermodynamic enolates are favored at higher temperatures. Under these conditions, the system is given more time to reach equilibrium, allowing for the formation of the more stable enolate that is energetically less favorable to form in a kinetically controlled reaction. In this case, the stabilization of the enolate is based on factors such as steric effects and the overall stability of the resulting product. Temperature thus plays a critical role in determining which enolate form predominates based on the reaction conditions applied, making it the key environmental factor influencing enolate selectivity.