Chair and Boat Conformations of Cyclohexane

Figures 6.11 and 6.12, pages 197 and 198

Chair Conformation

The chair conformation has no angle strain. It is staggered about each carbon-carbon bond, so it has no torsional strain either. It is strain free.

There are two types of hydrogens in the chair conformation. The bonds to the axial hydrogens (red) are parallel to the axis of the ring. Note how the axial bonds alternate in direction as one proceeds around the ring. The bonds to the equatorial hydrogens (blue) lie around the "equator" of the ring.

Boat Conformation

The boat conformation also has no angle strain. However, it does have torsional strain because the conformation is eclipsed at each of the green bonds. It also has some steric strain as a result of the interaction between the flagpole hydrogens (red). The boat conformation is 6 kcal/mol (25 kJ/mol) less stable than the chair conformation.

Twist Boat Conformation

Some of the strain in the boat conformation can be relieved by twisting it slightly. This introduces some angle strain, but relieves some of the torsional strain and some of the steric strain. The twist boat conformation is 1 kcal/mol (4 kJ/mol) more stable than the boat conformation, but it is still 5 kcal/mol (21 kJ/mol) less stable than the chair conformation.

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