My favorite groups of shapes are cupolas. Are there hydrocarbons in the shape of these similar to how cubane is to a cube? If so how stable are they, and could you please give some general information about each one.
They would be highly unstable due to the inverted tetrahedral geometry of the carbons in the top face. Generally, a polyhedron can form the basis of a stable hydrocarbon if it has at most 3 edges for each corner. A big caveat is that the hydrocarbon will distort the shape if the angle strain is too great. I found that out in my computational research on prismanes.
If one forgets about the correct mathematical notation for a moment:
- a cupola is like a bowl
- a bowl is a fragment of a spherical object
Molecules of this shape are found in the field of fullerenes (bucky balls).
The shape is more obvious in the following animation.
The structure of two extended bowl-shaped molecules has been published in J. Am. Chem. Soc., 2011, 133, 16319–16321 ( DOI), and although they are not true cupolas, you might find them interesting anyway.