If cyclohexane were planar, how much torsional strain would be present in the planar molecule? Assume that the energy cost for each H↔H eclipsing interaction is 4.0 kcal/mol.

Question

Quizplus · Accepted Answer

In a normal cyclohexane, the axial and equatorial hydrogens are staggered, which reduces torsional strain. However, if the molecule were planar, all of the hydrogens would be eclipsed, resulting in maximum torsional strain.

There are 12 pairs of H↔H eclipsing interactions in a planar cyclohexane. Since each interaction costs 4.0 kcal/mol of energy, the total torsional strain would be:

12 interactions × 4.0 kcal/mol/interaction = 48.0 kcal/mol = 48.0 kJ/mol

Therefore, the best choice is D, which is the closest to this calculated value.

If Cyclohexane Were Planar, How Much Torsional Strain Would Be