Question

The \(s p^{2}\) hybridization of the phenyl ring changes the hybridization of the oxygen in the \(\mathrm{O}-\mathrm{H}\) bond.

Short answer

Answer: The sp2 hybridization of the phenyl ring causes the oxygen atom in the O-H bond to change its hybridization from sp3 to sp2. This change occurs to facilitate the formation of a pi bond with an sp2-hybridized carbon atom in the phenyl ring.

Step-by-step solution

Understand the concept of hybridization

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals that are better suited for bonding in a molecule. The hybridization of an atom depends on the number of electron pairs around that atom - both bonding pairs and lone pairs.

Determine the initial hybridization of the phenyl ring

The phenyl ring is formed by a hexagonal arrangement of carbon atoms, each bonded to three neighboring atoms, with a delocalized pi electron system above and below the plane of the ring. Due to the arrangement of the atoms and the presence of pi electrons, each carbon atom in the phenyl ring is in sp2 hybridization.

Determine the initial hybridization of the oxygen atom in the O-H bond

The oxygen atom in O-H bond has two lone pairs and two bonds. Since an oxygen atom needs to have four orbitals (two for bonding and two for the lone pairs), it must undergo sp3 hybridization in order to accommodate the needed orbitals.

Analyze the interaction between the phenyl ring and the oxygen atom

When the oxygen atom approaches the phenyl ring, it needs an empty p orbital to form a pi bond with the sp2-hybridized carbon atom, which already has an empty p orbital as part of its pi electron system. To create an empty p orbital, one of the oxygen's lone pairs shifts to the p orbital, while the other remains as a lone pair. This shift converts one of the sp3 orbitals of the oxygen back into a p orbital.

Determine the new hybridization of the oxygen atom after interaction

After the formation of a pi bond with the phenyl ring's sp2-hybridized carbon atom, the oxygen atom has one bonding pair, one p-pi bond, one lone pair in the sp2 orbital, and one lone pair in the remaining p orbital. Therefore, after interaction, the oxygen atom undergoes sp2 hybridization as well. In conclusion, the sp2 hybridization of the phenyl ring not only maintains its own hybridization but also causes the oxygen atom in the O-H bond to change its hybridization from sp3 to sp2.

Key concepts

Understanding sp2 Hybridization

In chemistry, the concept of hybridization provides a way to explain the observed bonding patterns in molecules. Specifically, sp² hybridization occurs when one s orbital and two p orbitals from the same atom mix to create three hybrid orbitals of equivalent energy. These new orbitals lie on a plane and are separated by an angle of 120 degrees, which allows for the formation of trigonal planar structures in molecules.

For example, the carbon atoms in a phenyl ring undergo sp² hybridization. This type of hybridization allows each carbon to form three sigma bonds with neighboring atoms, and it also leaves one unhybridized p orbital. The unused p orbitals from different carbon atoms align parallel to each other and enable the formation of pi bonds, which are essential for the ring's stability and its unique chemical properties.

• sp² hybridized atoms have a planar geometric layout.
• Each atom has an unhybridized p orbital used for pi bonding.
• The energy of sp² hybrid orbitals is intermediate between s and p orbitals.

Understanding the nuances of sp² hybridization is crucial for predicting the behavior of molecules, like the reactivity of the phenyl ring with various substituents.

The Structure of the Phenyl Ring

A phenyl ring, also known as a benzene ring, is at the heart of many aromatic compounds in organic chemistry. It consists of six carbon atoms arranged in a hexagonal shape, with each carbon atom bonded to two neighboring carbon atoms and one hydrogen atom.

However, the phenyl ring is unique; it's not just a simple hexagon of single bonds. Each carbon atom contributes one of its p electrons to a delocalized system of electrons that resides above and below the plane of the ring. This delocalization provides extra stability to the ring, a concept known as aromaticity.

Characteristics of A Phenyl Ring:

• Composed of sp² hybridized carbon atoms
• Forms delocalized pi bonds throughout the structure
• Exhibits resonance, which distributes electrons across the entire ring

The phenyl ring's electrons are not located between just two atoms but are shared by all six carbons, resulting in a cloud of electron density often depicted by a circle within the hexagonal structure of the ring.

Pi Bond Formation and Characteristics

In molecular geometry, a pi bond is a form of covalent bond that arises from the side-to-side overlap of p orbitals. Unlike sigma bonds, which involve the end-to-end overlap of orbitals and allow free rotation about the bond axis, pi bonds do not permit such rotation due to their parallel overlap, which leads to the locked positions of bonded atoms.

A molecule may contain one or more pi bonds, often in conjunction with sigma bonds, creating a double or triple bond structure. Specifically, the phenyl ring features pi bonds that result from delocalized electrons between the sp² hybridized carbons. This delocalization creates a stable electron cloud that encompasses the entire ring.

Properties of Pi Bonds:

• Formed from parallel overlapping of p orbitals
• Exist in regions above and below the plane of the atomic nuclei
• Contribute to the rigidity and planar structure of molecules

Recognizing pi bonds is critical when deciphering the reactivity and physical properties of a compound, particularly in aromatic systems like the phenyl ring, where pi interactions play a vital role in chemical reactions.