Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.
(a)
(b)

Verified step by step guidance

1. Identify the functional groups in each compound. Both compounds in pair (b) are enolates, which are conjugate bases of enols.
2. Consider the resonance stabilization of the enolate ion. The more resonance structures available, the more stable the enolate ion, and thus the less basic it is.
3. Examine the position of the double bond in each enolate. In the first compound, the double bond is conjugated with the carbonyl group, allowing for resonance stabilization.
4. In the second compound, the double bond is not conjugated with the carbonyl group, which limits resonance stabilization.
5. Conclude that the enolate with the conjugated double bond (first compound) is more stable and therefore less basic. Thus, the second compound is more basic due to less resonance stabilization.

Key Concepts

Basicity of Amines

Basicity in organic chemistry refers to the ability of a compound to accept protons (H+ ions). Amines, which contain a nitrogen atom with a lone pair of electrons, are generally basic because they can donate this lone pair to bond with protons. The strength of an amine's basicity can be influenced by the surrounding molecular structure and the presence of electron-withdrawing or electron-donating groups.

Resonance Effects

Resonance refers to the delocalization of electrons in a molecule, which can stabilize certain structures. In the context of basicity, if an amine is part of a resonance-stabilized system, the lone pair on the nitrogen may be involved in resonance, making it less available to bond with protons. This can decrease the basicity of the amine compared to one where the lone pair is more localized and available.

Steric Hindrance

Steric hindrance occurs when bulky groups around a reactive site impede the approach of other molecules or ions. In the case of amines, if the nitrogen atom is surrounded by large substituents, it may be less accessible for protonation, thus reducing its basicity. Understanding the spatial arrangement of atoms in isomers is crucial for predicting their reactivity and basicity.