Question

what major type of strain does chair cyclohexane have compared to normal hexane?

A. Angle

B. Tortional

C. Face

D. Not a-d

Answer 1

Cyclohexane is considered a benchmark in determining ring strain in cycloalkanes and it is commonly accepted that there is little to no strain energy.^[1] In comparison, smaller cycloalkanes are much higher in energy due to increased strain. Cyclopropane is analogous to a triangle and thus has bond angles of 60°, much lower than the preferred 109.5° of an sp³ hybridized carbon. Furthermore, the hydrogens in cyclopropane are eclipsed. Cyclobutane experiences similar strain, with bond angles of approximately 88° (it isn't completely planar) and eclipsed hydrogens.

Perhaps surprisingly, medium-sized rings (7–13 carbons) experience more strain energy than cyclohexane. This transannular strain occurs when the cycloalkanes attempt to avoid angle and torsional strain. In doing so, CH₂ units across from each other are brought into proximity and experience Van der Waals strain.