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Ch.1 - Structure and Bonding
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
Chapter 1, Problem 54e

Predict the hybridization and geometry of the carbon and nitrogen atoms in the following molecules and ions. (Hint: Resonance.)
e. Chemical structure of a hexagonal ring with a nitrogen atom, illustrating hybridization and resonance concepts.

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1
Identify the structure: The molecule is a pyridinium ion, which is a six-membered aromatic ring with a nitrogen atom replacing one of the carbon atoms and a positive charge on the nitrogen.
Determine the hybridization of carbon atoms: In an aromatic ring like pyridine, each carbon atom is typically sp² hybridized. This is because each carbon forms three sigma bonds and has one unhybridized p orbital that participates in the pi system.
Determine the hybridization of the nitrogen atom: In the pyridinium ion, the nitrogen atom is also sp² hybridized. This is because it forms three sigma bonds (two with carbon atoms and one with a hydrogen atom) and has a lone pair that is delocalized in the aromatic pi system.
Predict the geometry around the carbon atoms: With sp² hybridization, the geometry around each carbon atom is trigonal planar, with bond angles of approximately 120 degrees.
Predict the geometry around the nitrogen atom: Similarly, with sp² hybridization, the geometry around the nitrogen atom is also trigonal planar, maintaining the aromaticity of the ring.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds. In organic chemistry, carbon typically undergoes sp3, sp2, or sp hybridization, affecting the molecule's geometry. For nitrogen in aromatic rings, sp2 hybridization is common due to resonance stabilization.
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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is determined by the hybridization of the central atom and the presence of lone pairs. For sp2 hybridized atoms, the geometry is typically trigonal planar, which is crucial for understanding the structure and reactivity of aromatic compounds.
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Resonance

Resonance is a concept where certain molecules can be represented by two or more valid Lewis structures, known as resonance structures. This delocalization of electrons stabilizes the molecule, affecting hybridization and geometry. In aromatic rings, resonance contributes to the stability and influences the hybridization of atoms like nitrogen.
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