Rank each set of compounds in order of increasing basicity.
(c) aniline, pyrrole, pyridine, piperidine

Verified step by step guidance

1. Step 1: Understand the concept of basicity. Basicity refers to the ability of a compound to donate a lone pair of electrons to accept a proton (H⁺). Factors affecting basicity include the availability of the lone pair, resonance effects, inductive effects, and hybridization of the nitrogen atom.
2. Step 2: Analyze aniline (structure i). Aniline has a nitrogen atom directly attached to a benzene ring. The lone pair on the nitrogen is partially delocalized into the aromatic ring via resonance, reducing its availability to accept a proton. This decreases its basicity.
3. Step 3: Analyze pyrrole (structure ii). Pyrrole is a five-membered aromatic ring with a nitrogen atom. The lone pair on the nitrogen is fully involved in maintaining the aromaticity of the ring, making it unavailable for protonation. Pyrrole is less basic than aniline.
4. Step 4: Analyze pyridine (structure iii). Pyridine is a six-membered aromatic ring with a nitrogen atom. The lone pair on the nitrogen is not involved in the aromaticity of the ring and is available for protonation. This makes pyridine more basic than both aniline and pyrrole.
5. Step 5: Analyze piperidine (structure iv). Piperidine is a six-membered saturated ring with a nitrogen atom. The nitrogen is sp³ hybridized, and its lone pair is fully available for protonation without any resonance effects. This makes piperidine the most basic compound in the set.

Key Concepts

Basicity in Organic Chemistry

Basicity refers to the ability of a compound to accept protons (H+) in a chemical reaction. In organic chemistry, basicity is influenced by the availability of a lone pair of electrons on a nitrogen atom, which can bond with protons. The strength of a base is often compared using pKa values, where lower pKa indicates a stronger base.

Aromaticity and Electron Delocalization

Aromatic compounds, such as pyridine and pyrrole, exhibit unique stability due to electron delocalization within a cyclic structure. This delocalization can affect basicity; for instance, in pyrrole, the nitrogen's lone pair is involved in the aromatic system, making it less available for protonation compared to pyridine, where the lone pair is more accessible.

Steric and Electronic Effects

Steric effects arise from the spatial arrangement of atoms in a molecule, which can hinder or facilitate interactions with protons. Electronic effects, such as inductive and resonance effects, influence the electron density around the nitrogen atom. For example, piperidine, a saturated nitrogen-containing compound, is more basic than aniline due to less steric hindrance and greater availability of the lone pair for protonation.