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tetrahedrane

n. (context organic compound English) hypothetically, one of the Platonic hydrocarbons, C4H4, having the carbon atoms at the vertices of a tetrahedron; has not yet been synthesized, and would be very unstable.

Wikipedia
Tetrahedrane

Tetrahedrane is a platonic hydrocarbon with chemical formula and a tetrahedral structure. Extreme angle strain (carbon bond angles deviate considerably from the tetrahedral bond angle of 109.5°) prevents this molecule from forming naturally.