Explain why the hydration of ethylene (Eq 4.44) is a very slow reaction. (Hint: Think about the

step 1 So why is benzene so much more stable than ethylene? Well, we can go ahead and draw benzene righ

Explain why the hydration of ethylene (Eq 4.44) is a very...

Key Concepts

Activation Energy and Reaction Kinetics

The rate of a chemical reaction is heavily influenced by the activation energy—the energy difference between the reactants and the transition state. When the formation of a reactive intermediate requires high energy, as indicated by the structure of the intermediate under study, the reaction will proceed slowly due to the large energy barrier.

Hydration Reaction Mechanism

The hydration of alkenes generally involves an electrophilic addition mechanism that typically forms a charged intermediate. The nature and structure of this intermediate, combined with the stability considerations and energy profile predicted by Hammond's postulate, explain the observed slow reaction rate under standard conditions.

Hammond's Postulate

Hammond's postulate relates the structure of the transition state of a reaction to the structures of the nearest stable species (reactants or products). It suggests that if a reaction step is endothermic, the transition state resembles the products, which in the case of generating an unstable intermediate means the transition state will be higher in energy. This can severely slow down the reaction rate since the energy barrier to overcome is high.

Carbocation Intermediate Stability

In reactions that proceed through carbocation intermediates, the stability of these intermediates is a key factor in determining the reaction rate. The formation of a less stable or high-energy carbocation leads to a higher activation energy for the reaction, resulting in a slow reaction process.

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