In the rearrangement of 4,4 -diphenylcyclocyclohex-2-enone...

Name: Problem 14, Chapter 12: Advanced Organic Chemistry. Part A. Structure and Mechanisms
Uploaded: 2020-05-28T21:26:38-08:00
Duration: 2 min 15 s
Channel: Mercedes Mazza
Description: In the rearrangement of 4,4 -diphenylcyclocyclohex-2-enone to 5,6 diphenylbicyclo[3.1.0]hexan-2-one, there is a strong preference for formation of the endo phenyl stereoisomer. Offer an explanation for this stereoselectivity.

In the rearrangement of 4,4 -diphenylcyclocyclohex-2-enone to 5,6 diphenylbicyclo[3.1.0]hexan-2-one, there is a strong preference for formation of the endo phenyl stereoisomer. Offer an explanation for this stereoselectivity.

Key Concepts

Stereoselectivity

Stereoselectivity refers to the preferential formation of one stereoisomer over others in a chemical reaction. This outcome is governed by factors such as the relative energies of competing transition states and steric as well as electronic effects that make one pathway more favorable than another.

Endo versus Exo Stereochemistry

In bicyclic and polycyclic systems, endo and exo denote the orientation of substituents relative to the core framework, typically with the endo orientation pointing inward toward the cyclo structure. Reactions frequently favor the endo product due to favorable secondary orbital interactions or a transition state geometry that minimizes steric repulsion and enhances orbital overlap.

Transition State Stabilization

Transition state stabilization involves lowering the energy barrier of a reaction pathway through favorable interactions during the transition state. In stereoselective reactions, such as rearrangements, the transition state leading to one stereoisomer can be stabilized by secondary orbital interactions or minimized steric strain, thereby dictating the preferred formation of that product.

Rearrangement Mechanisms

Rearrangement mechanisms are processes in which the connectivity of atoms in a molecule is reorganized, often through concerted or stepwise pathways. The specific stereochemical outcome in these reactions is highly dependent on the geometric and electronic structure of the transition state, which can channel the reaction to favor one isomer over another.

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