Within each structure, rank the indicated nitrogens by increasing basicity.
(c)

Verified step by step guidance

1. Step 1: Understand the concept of basicity. Basicity refers to the ability of a nitrogen atom to donate its lone pair of electrons to a proton (H⁺). Factors affecting basicity include resonance, inductive effects, hybridization, and steric hindrance.
2. Step 2: Analyze nitrogen A. Nitrogen A is part of an aromatic ring system and is involved in resonance with the π-electrons of the ring. This delocalization reduces the availability of its lone pair for protonation, making it less basic.
3. Step 3: Analyze nitrogen B. Nitrogen B is part of an aliphatic amine group. It is not involved in resonance and has its lone pair readily available for protonation. Additionally, the alkyl groups attached to nitrogen B exert an electron-donating inductive effect, increasing its basicity.
4. Step 4: Analyze nitrogen C. Nitrogen C is part of a nitrile group (-C≡N). The triple bond between carbon and nitrogen is highly electronegative, pulling electron density away from nitrogen C. This makes nitrogen C's lone pair less available for protonation, significantly reducing its basicity.
5. Step 5: Rank the nitrogens by increasing basicity. Based on the analysis, nitrogen C (nitrile group) is the least basic, followed by nitrogen A (aromatic ring), and nitrogen B (aliphatic amine) is the most basic.

Key Concepts

Basicity of Amines

Basicity in amines refers to the ability of a nitrogen atom to donate a lone pair of electrons to a proton (H+). The basicity of an amine is influenced by the electron-donating or withdrawing effects of substituents attached to the nitrogen. Generally, more electron-donating groups increase basicity, while electron-withdrawing groups decrease it.

Resonance Effects

Resonance effects occur when electron density is delocalized across multiple atoms, which can stabilize or destabilize a molecule. In the context of basicity, if a nitrogen atom is part of a resonance structure that delocalizes its lone pair, its ability to donate that pair decreases, leading to lower basicity. Understanding how resonance affects the nitrogen atoms in the given structures is crucial for ranking their basicity.

Steric Hindrance

Steric hindrance refers to the repulsion between bulky groups in a molecule that can affect reactivity and stability. In amines, steric hindrance can impede the approach of protons to the nitrogen atom, thereby affecting its basicity. When ranking the basicity of the nitrogens in the provided structures, considering the spatial arrangement of substituents around each nitrogen is essential.