There is a high barrier to rotation around a carbon-carbon...

Name: Problem 92, Chapter 11: Chemistry and Chemical Reactivity
Uploaded: 2020-06-15T17:56:46-08:00
Duration: 2 min 58 s
Channel: Sydney Atkins
Description: There is a high barrier to rotation around a carbon-carbon double bond, whereas the barrier to rotation around a carbon-carbon single bond is very small. Use the orbital overlap model of bonding (Chapter 10 ) to explain why restricted rotation occurs around a double bond.

There is a high barrier to rotation around a carbon-carbon double bond, whereas the barrier to rotation around a carbon-carbon single bond is very small. Use the orbital overlap model of bonding (Chapter 10 ) to explain why restricted rotation occurs around a double bond.

Key Concepts

Pi Bonding

A pi bond arises from the side-by-side overlap of parallel p orbitals, positioned above and below the plane of the atoms involved. This type of bond is sensitive to rotation because any twist away from the optimal parallel alignment of the p orbitals significantly reduces the overlap, thereby breaking the pi bonding interaction.

Rotation Barrier

The restriction of rotation around a double bond is primarily due to the presence of a pi bond. Rotation would disrupt the necessary parallel alignment of the p orbitals that form the pi bond, leading to a high energy barrier. In contrast, rotation around a single bond, which is a sigma bond, remains feasible since the overlap necessary for sigma bonding can be maintained through rotation.

Orbital Overlap

The orbital overlap model explains chemical bonding by considering the spatial arrangement and interaction of atomic orbitals. In this context, the quality of the overlap between orbitals (such as p orbitals) directly affects the strength and properties of the bonds formed, including whether rotation is feasible or restricted.

Sigma Bonding

A sigma bond is formed by the head?to?head overlap of orbitals, typically s or p orbitals, along the internuclear axis. Sigma bonds allow for free rotation because the overlapping orbitals maintain sufficient overlap regardless of the rotational alignment of the bonded atoms.

Transcript

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