Chapter 17, Problem 17.13YT

Interpretation Introduction

Interpretation:

Which product of the given nucleophilic addition reaction is the thermodynamic product and which one is kinetic product is to be explained.

Concept introduction:

In the case of $\text{α,β-}$ unsaturated carbonyl compounds, the weak resonance contributor with separated charges generates a small partial positive charge on the $\text{β}$ carbon due to the resonance hybrid. Thus, a nucleophile can attack at either the carbonyl carbon or the $\text{β}$ carbon. Polar $\text{π}$ bonds of $\text{α,β-}$ unsaturated carbonyl compounds are susceptible to nucleophilic attack at both the electron-poor atom of the polar $\text{π}$ bond and the $\text{β}$ carbon. Attack at the carbonyl carbon yields the direct addition (or $\text{1, 2-addition}$) product whereas attack at the beta carbon yields the conjugate addition (or $\text{1, 4-addition}$). Direct addition to an $\text{α,β-}$ unsaturated polar $\text{π}$ bond dominates if the nucleophile adds irreversibly to the polar carbonyl bond, and when $\text{1, 4-addition}$ takes place, the nucleophile adds to the $\text{β}$ carbon and reversibly to the carbonyl group. Generally, the conjugate addition product is more stable and also called thermodynamic product, and the direct addition product is one that is formed more rapidly (so requires lower energy barrier), which is the kinetic product.