This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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You're on a roll — Step 1: Apply Hückel's Rule to Pyridine. Hückel's rule states that a compound is aromatic if it is cyclic, planar, fully conjugated, and has (4n+2) electrons, where n is a non-negative integer. Cyclic and Planar: Pyridine is a 6-membered heterocyclic ring that is planar. Fully Conjugated: All 6 atoms (5 carbons and 1 nitrogen) are sp^2 hybridized, each contributing a p-orbital to the cyclic system. Number of electrons: Pyridine has three double bonds within the ring, contributing 3 × 2 = 6 electrons. The lone pair on the nitrogen atom is in an sp^2 orbital, perpendicular to the system, and does not contribute to the aromaticity. Hückel's Rule: With 6 electrons, we can set 4n+2 = 6. 4n = 4 n = 1 Since n=1 is an integer, pyridine is aromatic. Step 2: Discuss the heteroatom's contribution in Pyridine. The nitrogen atom in pyridine is sp^2 hybridized. It contributes one electron to the system through its p-orbital, forming part of a double bond. Its lone pair of electrons is localized in an sp^2 orbital that lies in the plane of the ring and is not part of the aromatic system. This lone pair is available for protonation, making pyridine a base. The electronegativity of nitrogen withdraws electron density from the ring, making pyridine less reactive towards electrophilic aromatic substitution compared to benzene. Step 3: Apply Hückel's Rule to Furan. Cyclic and Planar: Furan is a 5-membered heterocyclic ring that is planar. Fully Conjugated: All 5 atoms (4 carbons and 1 oxygen) are sp^2 hybridized, each contributing a p-orbital. Number of electrons: Furan has two double bonds within the ring, contributing 2 × 2 = 4 electrons. The oxygen atom has two lone pairs. One lone pair is in an sp^2 orbital, but the other* lone pair occupies a p-orbital that aligns with the p-orbitals of the carbon atoms, contributing 2 electrons to the cyclic system. Hückel's Rule: Total electrons = 4 + 2 = 6. We can set 4n+2 = 6. 4n = 4 n = 1 Since n=1 is an integer, furan is aromatic. Step 4: Discuss the heteroatom's contribution in Furan. The oxygen atom in furan is sp^2 hybridized. It contributes two electrons from one of its lone pairs to the aromatic system, which occupies a p-orbital. The other lone pair is in an sp^2 orbital and is not part of the system. The contribution of these two electrons from oxygen makes furan an electron-rich aromatic system, which is more reactive towards electrophilic aromatic substitution compared to benzene. The final answers are: Pyridine is aromatic because it is cyclic, planar, fully conjugated, and has 6 electrons (4n+2 with n=1). The nitrogen's lone pair is not part of the system. Furan is aromatic because it is cyclic, planar, fully conjugated, and has 6 electrons (4n+2 with n=1). One of the oxygen's lone pairs contributes to the system. Got more? Send 'em 📸