What would cyclopropane look like if it weren't planar?

How and why does non-planar cyclopropane have higher torsional strain than planar cyclopropane? can you please show me visually via image that non-planar cyclopropane has higher torisional strain and maybe more angle strain than planar cyclopropane?

On the otherhand, why and how is cyclobutane bulged or puckering, a.k.a non-planar?

  • 12
    $\begingroup$ Considering that three points define a plane, geometrically, it's not really possible for cyclopropane to be non-planar... $\endgroup$ – a-cyclohexane-molecule Oct 17 '16 at 4:31

Why is cyclopropane planar?

This is like asking why $\ce{HCl}$ is linear–just as two points define a line, three points define a plane. There isn't any way to orient the three methylene groups in space that they aren't coplanar.


Torsional strain in cyclopropane is also significant for this reason (the molecule has a $\mathrm{C_3}$ axis through the center of the ring, meaning every hydrogen is overlapping). Any reduction in torsional strain, however, decreases the already weak carbon-carbon $\ce{sp^3}$ orbital overlap. Though the $\ce{C-C-C}$ bond angles are $60º$, the orbitals are still oriented roughly $109.5º$ from one another, resulting in very weak and highly strained banana bonds.


Why is cyclobutane nonplanar?

Cyclobutane has one additional methylene, and can reduce its torsional strain by orienting one methylene out of the plane of the other three.


This is in part possible due to the much greater carbon-carbon $\ce{sp^3}$ orbital overlap.

| improve this answer | |
  • $\begingroup$ Due to symmetry, the carbon in cyclopropane is not $sp^3$ but $sp^2$ hybridized. $\endgroup$ – Deathbreath Nov 14 '16 at 19:03

If cyclopropane did pucker then a new plane would exist. This is because any set of three points (a.k.a three carbons) is coplanar. Cyclobutane puckering can occur and make a difference as a set of four points/carbons is not necessarily coplanar.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.