Which conformation is the most stable form of cyclohexane?

Which conformation is the most stable form of cyclohexane?

• A. Envelope
• B. Butterfly
• C. Boat
• D. Chair

Answer: (D)

Minimizing strain in the ring is what makes a conformation most stable. In the chair form, every C–C bond is staggered with respect to its neighbors, so there are no eclipsing interactions between adjacent bonds. The bond angles stay close to the ideal tetrahedral angle (about 109.5 degrees), keeping angle strain to a minimum. This combination—no torsional (eclipsing) strain and minimal angle strain—lets the chair sit at the lowest energy. The other shapes introduce more strain. The boat form has significant torsional strain from eclipsing interactions between hydrogens on the bow and stern, plus destabilizing contacts between other axial and equatorial hydrogens and carbons. Those interactions raise the energy, so the boat is less stable than the chair. The envelope and butterfly are not realistic low-energy forms for a six-membered ring; they would force atoms into awkward angles and increase eclipsing contacts, making them much higher in energy. So, the chair form is the most stable because it achieves the least overall strain by keeping bonds staggered and angles near ideal.

Minimizing strain in the ring is what makes a conformation most stable. In the chair form, every C–C bond is staggered with respect to its neighbors, so there are no eclipsing interactions between adjacent bonds. The bond angles stay close to the ideal tetrahedral angle (about 109.5 degrees), keeping angle strain to a minimum. This combination—no torsional (eclipsing) strain and minimal angle strain—lets the chair sit at the lowest energy.

The other shapes introduce more strain. The boat form has significant torsional strain from eclipsing interactions between hydrogens on the bow and stern, plus destabilizing contacts between other axial and equatorial hydrogens and carbons. Those interactions raise the energy, so the boat is less stable than the chair. The envelope and butterfly are not realistic low-energy forms for a six-membered ring; they would force atoms into awkward angles and increase eclipsing contacts, making them much higher in energy.

So, the chair form is the most stable because it achieves the least overall strain by keeping bonds staggered and angles near ideal.