Two nitrogen-containing bases are shown.
• Pyridine: an sp2-hybridized N atom in an aromatic ring
• Piperidine: a saturated six-membered ring containing an sp3-hybridized N atom
Standard aqueous conditions apply.
(1) Determine which of the two bases is the stronger base in water.
(2) Explain your answer in part (a) with reference to hybridization, lone-pair availability, and any resonance interactions.
(3) Compare the pKa values of the respective conjugate acids. Which conjugate acid is stronger, and why?
(4) Predict qualitatively how substitution of a nitro group at the 4-position of pyridine would alter the basicity of the ring nitrogen. Provide a structural rationale.