What ring size is stable? How can I tell if it should be planar?
Don't be fooled: 1,3,5,7-cyclooctatetraene is actually NOT planar.
Here is the "tub"-shaped structure elucidated by Kaufman, Fankuchen, and Mark using X-ray Diffraction in 1948:
However, on either side of the spectrum, you can have an unstable
For instance, cyclopropene, a three-membered ring, is VERY unstable, having a
Cyclobutadiene, a four-membered ring, has been proposed to not be a perfect square, but rectangular.
As a general rule of thumb, if a conjugated polyene ring has more than