Answer to Question #104929 in Organic Chemistry for Rakesh kumar

Question

Draw and explain the energy profile associated with ring flipping of chair conformation of cyclohexane.

Answer 1

• The chair conformation has the lowest energy, as it has the lowest values for angular and torsional strain (they are both equal to zero).
• The half-chair conformation has the highest energy - due to high angular strain and eclipsed conformation for hydrogens in the flipping part of the molecule (high torsional strain). In fact, half-chair is a transition state between chair and twist boat conformation.
• The twist boat conformation has higher energy than chair conformation due to unfavorable position of the hydrogens (they are partially eclipsed) and slight angle strain. Also, there is an interaction between hydrogens attached to the first and fourth carbon atoms (the "flagpole" hydrogens). This type of strain called van der Waals strain.
• The boat conformation is a transition state between two twist boat conformations. Such conformation has higher energy than a twist boat due to unrelieved torsional and van der Waals strain.
• The second twist boat conformation later can transform into chair conformation through the half-chair conformation.